Add comprehensive URL builder for OpenDAP endpoints

Implements a builder pattern for constructing OpenDAP URLs with support for DAS, DDS, and DODS endpoints, including full constraint expression support for subsetting data following DAP2 standards.

🤖 Generated with [opencode](https://opencode.ai)

Co-Authored-By: opencode <noreply@opencode.ai>

Author: mpiannucci

readap/src/lib.rs

@@ -3,7 +3,9 @@ pub mod data;
 pub mod dds;
 pub mod dods;
 pub mod errors;
+pub mod url_builder;
 
 pub use das::*;
 pub use dds::*;
 pub use dods::*;
+pub use url_builder::*;