Add Google Test suite for regression testing baseline.

[fdcastel]

Summary

Adds a comprehensive Google Test suite (375 tests across 38 test suites) that exercises the Firebird ODBC driver through the standard ODBC API via the Driver Manager. This establishes a regression testing baseline on the current, unmodified driver — per the plan discussed in PR #275.

No driver source code is modified by this PR.

Motivation

Before making any code changes (bugfixes, build system, CI), we need a testing baseline that documents what the current driver can do and where improvements are needed. This test suite:

1. Verifies existing functionality — 230 tests pass, confirming data types, parameter binding, cursors, catalog functions, etc. all work correctly.
2. Documents known gaps — 145 tests are marked GTEST_SKIP() with explanations of what improvement they require (e.g., "Requires Phase 7 (OC-1): SQLCopyDesc null records crash fix").
3. Provides a regression gate — future PRs can remove individual GTEST_SKIP() markers as fixes are merged, turning them into pass/fail tests.

What's included

Infrastructure

File	Description
tests/CMakeLists.txt	Standalone CMake project; fetches Google Test v1.14.0 via FetchContent
tests/test_main.cpp	GTest entry point
tests/test_helpers.h	OdbcConnectedTest fixture, TempTable RAII guard, error helpers
tests/README.md	Build/run instructions, test categories, connection string format

Test files (30 files)

Category A — Tests that pass on vanilla master (16 files)

File	Description
test_data_types.cpp	All SQL data types: INTEGER, VARCHAR, NUMERIC, DATE, TIME, TIMESTAMP, etc.
test_result_conversions.cpp	SQLGetData type conversions
test_param_conversions.cpp	SQLBindParameter type conversions
test_prepare.cpp	SQLPrepare / SQLExecute lifecycle
test_cursors.cpp	Cursor behavior across statements
test_cursor_commit.cpp	Cursor behavior across transactions
test_cursor_name.cpp	SQLSetCursorName / SQLGetCursorName
test_data_at_execution.cpp	SQL_DATA_AT_EXEC / SQLPutData
test_array_binding.cpp	Column-wise + row-wise parameter arrays
test_bindcol.cpp	Dynamic unbind/rebind mid-fetch
test_descrec.cpp	SQLGetDescRec for all column types
test_blob.cpp	BLOB read/write (small, large, NULL)
test_multi_statement.cpp	Multiple statement handles on one connection
test_stmthandles.cpp	Stress test: 100+ simultaneous statement handles
test_wchar.cpp	SQL_C_WCHAR bind/fetch and truncation
test_escape_sequences.cpp	ODBC escape sequence passthrough

Category B — Mixed pass/skip (6 files)

These files contain tests that pass and tests that are GTEST_SKIP()'d because they depend on driver improvements not yet merged.

File	Pass	Skip	Skip reason
test_descriptor.cpp	6	7	SQLCopyDesc crash, SetDescCount allocation
test_connect_options.cpp	6	30	CONNECTION_TIMEOUT, ASYNC_ENABLE, QUERY_TIMEOUT, RESET_CONNECTION
test_errors.cpp	11	7	SQL_DIAG_ROW_COUNT, string truncation indicator
test_catalogfunctions.cpp	26	3	SQLGetTypeInfo ordering, GUID searchability
test_server_version.cpp	4	2	FB4+ type info detection
test_scrollable_cursor.cpp	5	4	Scrollable cursor edge cases

Category C — All tests SKIP'd (8 files)

These files test features that don't exist on vanilla master. Every test is GTEST_SKIP()'d with an explanation.

File	Tests	Feature required
test_null_handles.cpp	65	Crash prevention: NULL handle validation
test_savepoint.cpp	4	Savepoint transaction isolation
test_conn_settings.cpp	3	ConnSettings DSN attribute
test_odbc38_compliance.cpp	12	ODBC 3.8 (SQL_OV_ODBC3_80, RESET_CONNECTION)
test_guid_and_binary.cpp	14	SQL_GUID type mapping, FB4+ types
test_odbc_string.cpp	26	OdbcString class (guarded with __has_include)
test_phase7_crusher_fixes.cpp	—	Not compiled (documentation only, tests duplicated in Cat B files)
test_phase11_typeinfo_timeout_pool.cpp	—	Not compiled (documentation only, tests duplicated in Cat B files)

How to build and run

Prerequisites

• The Firebird ODBC driver must be pre-built (from Builds/MsVc2022.win/OdbcFb.sln) and registered as an ODBC data source
• A Firebird 3.0+ database must be accessible
• CMake ≥ 3.14

Build

cmake -B build-tests -S tests
cmake --build build-tests --config Release

Run

rem Windows
set FIREBIRD_ODBC_CONNECTION=Driver={Firebird ODBC Driver};Dbname=localhost:C:\path\to\test.fdb;Uid=SYSDBA;Pwd=masterkey;
ctest --test-dir build-tests --output-on-failure -C Release

Expected output

[==========] 375 tests from 38 test suites ran.
[  PASSED  ] 230 tests.
[  SKIPPED ] 145 tests.
[  FAILED  ] 0 tests.

Without FIREBIRD_ODBC_CONNECTION set, all 375 tests skip gracefully.

Design decisions

1. Standalone CMake project — Since there's no root CMakeLists.txt yet (that's a future PR), the test suite is self-contained with its own project() declaration. It will integrate via add_subdirectory(tests) when a root CMake build is added.

2. Tests via Driver Manager, not direct DLL calls — Tests link against odbc32/odbccp32 (the Windows ODBC Driver Manager) and connect using a standard connection string. This tests the driver as applications actually use it. The one exception is test_null_handles.cpp (which loads the DLL directly to test entry-point validation) — all its tests are SKIP'd.

3. GTEST_SKIP() preserves test code — Rather than deleting tests that don't pass on vanilla, each is wrapped with GTEST_SKIP() << "reason". The test code remains intact so that future PRs can simply remove the SKIP line to activate the test.

4. No driver code changes — This PR adds only the tests/ directory. No existing source files are modified.

Checklist

• Tests build with CMake 3.14+ / MSVC 2022
• 230 tests pass against vanilla Firebird ODBC driver
• 145 tests skip with clear explanations
• 0 test failures
• Graceful SKIP when no database connection is available
• README with build and run instructions

[fdcastel]

Pushed fixes for four issues identified in @irodushka’s review.