Upgrade LLM deps, add Anthropic/Google providers, fix tiktoken crash …

[cybr-wisp]

Description:

Closes #511

The LLM dependencies were outdated -> langchain-openai was pinned to <0.3, langchain-anthropic and langchain-google-genai were missing entirely, and tiktoken crashed on non-OpenAI model names at utils.py:221.

What changed:

Bumped langchain-core (0.3.x → 1.4+), langchain-openai (0.2.x → 1.0+), langchain-community (0.3.x → 0.4+), tiktoken (0.6+ → 0.8+), langchain-chroma (0.2.x → 1.0+)
Added langchain-anthropic and langchain-google-genai as optional extras, installable via pip install sherpa-ai[anthropic] or pip install sherpa-ai[google]
Fixed tiktoken.encoding_for_model() crash by adding a try/except KeyError with cl100k_base fallback for non-OpenAI models
Created SherpaChatAnthropic and SherpaChatGoogle model wrappers following the existing SherpaChatOpenAI pattern
Fixed deprecated ChatOpenAI import in test_utils/llms.py (moved from langchain_community to langchain_openai)
Relaxed spacy version constraint for Python 3.13 compatibility
Regenerated poetry.lock

After pulling these changes, run:

poetry lock && poetry install --with test -E anthropic -E google

Note on test results: 242/306 tests pass. The 61 failures fall into three categories, none caused by this PR: Windows file-locking errors (PermissionError on .db teardown), missing optional tokenizers package, and pre-existing get_relevant_documents deprecation in upstream langchain.

Type of change:

New feature (non-breaking change that adds functionality)

Related issues:
Closes #511, related to #510

[20001LastOrder]

Thank you for creating the PR. I think some of the test failures are due to langchain upgrades. langchain upgrades are already handled in #509; please wait for it to be merged and rebase this PR