fix: adapt UiPathChatAnthropic to the langchain-anthropic 1.7.0 raw-response contract

[andreibalas-uipath]

What changed and why

Follow-up to #132, which pinned langchain-anthropic<1.7.0 as an interim mitigation. This PR is the real fix: it adapts UiPathChatAnthropic to the langchain-anthropic 1.7.0 contract and lifts the pin.

• UiPathChatAnthropic._create/._acreate now route through with_raw_response.create(...) (both the plain and betas branches). langchain-anthropic 1.7.0 changed these private methods to return a raw-response wrapper and calls .parse() on the result in _generate/_agenerate/_stream/_astream; the previous override bodies returned parsed objects, so every operation failed with 'Message'/'Stream'/'AsyncStream' object has no attribute 'parse'.
• langchain-anthropic bound on the anthropic and bedrock extras moves from >=1.4.1,<1.7.0 (the fix: bound langchain-anthropic<1.7.0 in uipath-langchain-client #132 pin) to >=1.7.0,<2.0.0.
• UiPathChatLiteLLM no longer lets ChatLiteLLM's before-validator mark streaming=False as explicitly set: langchain-core >= 1.4 (pulled in by the lock refresh) treats that as a hard streaming opt-out, silently downgrading .stream()/.astream() to non-streaming invokes.
• New tests: tests/langchain/clients/anthropic/test_raw_response_contract.py (mocked-transport coverage of invoke/stream/tool-calling/structured-output, sync+async, the betas routing branch, and gateway-metadata extraction off the raw wrapper) and tests/langchain/clients/litellm/test_streaming_dispatch.py.

Affected packages

• uipath-langchain-client only (1.18.3 → 1.18.4). Core untouched.

Verification

• ruff check, ruff format --check, pyright clean; full suite green (2110+ passed, cassette replay).
• With main's code + langchain-anthropic 1.7.0, the Anthropic suite fails 121 tests with exactly the errors from the uipath-langchain-python chat-models CI failure ('Message' object has no attribute 'parse', etc.); with this branch it passes 133/133, including the VCR integration tests replaying recorded gateway traffic for the same model/config the failing CI testcase uses (anthropic.claude-haiku-4-5-20251001-v1:0, vendor_type="awsbedrock").

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