Content block tokens supported in callbacks

Changes since langchain-classic==1.0.7

release(langchain-classic): 1.0.8 (#38033) hotfix(core): bump lockfile(s) (#38032) fix(core): support content block tokens in callbacks (#34739) chore(core): improve typing of Runnable __or__ (#34530) hotfix(openai): min core dep (#37990) chore: bump pyarrow from 21.0.0 to 23.0.1 in /libs/langchain (#37929) chore: bump starlette from 0.49.1 to 1.0.1 in /libs/langchain (#37899) test(langchain,partners): disable pytest-benchmark under xdist to silence PytestBenchmarkWarning (#37901) chore: bump aiohttp from 3.13.4 to 3.14.0 in /libs/langchain (#37889) chore(infra): bump langchain-tests floor to 1.1.9 (#37610) release(standard-tests): 1.1.9 (#37609) chore: bump idna from 3.10 to 3.15 in /libs/langchain (#37537) ci(infra): harden Dependabot version-bound preservation (#37510) hotfix: bump lockfiles (#37508) chore: bump langsmith from 0.7.31 to 0.8.0 in /libs/langchain (#37393) chore(infra): merge v1.4 into master (#37350) chore: bump urllib3 from 2.6.3 to 2.7.0 in /libs/langchain (#37327) chore: bump mistune from 3.1.4 to 3.2.1 in /libs/langchain (#37236)