File-search results confined; allowed prefixes tightened

Changes since langchain-anthropic==1.4.5

release(anthropic): 1.4.6 (#38105) fix(langchain,anthropic): confine file-search results and tighten anthropic allowed_prefixes (#38106) release(core): 1.4.6 (#38061) feat(core,partners): add package version tracking to tracing metadata (#35295) chore(infra): bump mypy to 2.1 and unify type-check config across the monorepo (#36470) feat(standard-tests): validate tool call chunks during streaming (#34707) test(anthropic): make expected warnings explicit (#38044) test(anthropic): make tests robust to gateway base URL (#38043)