refactor(langchain): refactor optional imports logic in `langchain_v1` #46084

Job	Run time
Detect Changes & Set Matrix	19s
test-doc-imports	0s
Extended Tests (libs/langchain_v1, 3.13)	37s
Extended Tests (libs/langchain, 3.13)	31s
Extended Tests (libs/langchain, 3.9)	33s
Extended Tests (libs/langchain_v1, 3.10)	36s
test (libs/langchain, 3.13) / Python 3.13	43s
test (libs/langchain_v1, 3.10) / Python 3.10	29s
test (libs/langchain, 3.9) / Python 3.9	37s
lint (libs/langchain, 3.13) / Python 3.13	1m 33s
lint (libs/langchain, 3.9) / Python 3.9	1m 20s
lint (libs/langchain_v1, 3.10) / Python 3.10	59s
test (libs/langchain_v1, 3.13) / Python 3.13	37s
lint (libs/langchain_v1, 3.13) / Python 3.13	42s
test-pydantic (libs/langchain, 2.8.0, 3.11) / Pydantic ~=2.8.0	29s
test-pydantic (libs/langchain_v1, 2.10.0, 3.11) / Pydantic ~=2.10.0	31s
test-pydantic (libs/langchain, 2.10.0, 3.11) / Pydantic ~=2.10.0	28s
test-pydantic (libs/langchain_v1, 2.7.0, 3.11) / Pydantic ~=2.7.0	36s
test-pydantic (libs/langchain_v1, 2.11.0, 3.11) / Pydantic ~=2.11.0	32s
test-pydantic (libs/langchain, 2.7.0, 3.11) / Pydantic ~=2.7.0	32s
test-pydantic (libs/langchain_v1, 2.8.0, 3.11) / Pydantic ~=2.8.0	31s
test-pydantic (libs/langchain_v1, 2.9.0, 3.11) / Pydantic ~=2.9.0	31s
test-pydantic (libs/langchain, 2.9.0, 3.11) / Pydantic ~=2.9.0	29s
compile-integration-tests (libs/langchain, 3.13) / Python 3.13	21s
compile-integration-tests (libs/langchain, 3.9) / Python 3.9	23s
compile-integration-tests (libs/langchain_v1, 3.13) / Python 3.13	22s
compile-integration-tests (libs/langchain_v1, 3.10) / Python 3.10	22s
✅ CI Success	3s
	15m 46s

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