fix(llm): replace retry with tenacity in ollama.py

[bitflicker64]

Summary

ollama.py was using the abandoned retry PyPI package (last maintained 2016)
while openai.py and litellm.py in the same directory already use tenacity.
This PR brings ollama.py in line with the established patterns.

Changes

hugegraph-llm/src/hugegraph_llm/models/llms/ollama.py

• Replace from retry import retry with tenacity imports
• Replace @retry(tries=3, delay=1) with stop_after_attempt(3),
  wait_exponential(min=4, max=10), and
  retry_if_exception_type((ollama.ResponseError, httpx.ConnectError, httpx.TimeoutException))
  — matching the pattern in openai.py
• Narrow except Exception to the specific retriable exception types
• Replace print(f"Retrying LLM call {e}") with log.error(...) (consistent
  with openai.py; log was already imported and used in the same file)
• Fix misleading "Retrying LLM call" message in agenerate_streaming,
  which has no @retry decorator
• Replace """Comment""" placeholder docstrings with real descriptions

hugegraph-llm/pyproject.toml

• Remove "retry", add "tenacity" as an explicit dependency

pyproject.toml

• Replace "retry~=0.9.2" constraint with "tenacity~=8.5.0"

Closes #365

[imbajin]

Blocking: yes. Summary: The Ollama retry policy changes need deterministic regression coverage. Evidence: uv run ruff check . passed; existing Ollama tests are external-service tests and do not cover the new Tenacity retry predicate.

[imbajin]

⚠️ Add regression coverage for the new retry policy

This changes both the retry library and the retry predicate/delay for generate() and agenerate(), but the PR does not add a mock-based test for retryable Ollama/httpx failures or for non-retryable errors. The module guidance asks code changes to cover changed behavior; please add a deterministic unit test that stubs client.chat / async_client.chat so CI proves the new Tenacity policy is wired correctly without requiring an Ollama service.

[bitflicker64]

second commit adds TestOllamaClientRetryPolicy: mock-based, no live service, covers retryable/non-retryable exceptions and transient recovery for both generate() and agenerate().

[imbajin]

Blocking: no. Summary: No obvious issues found in the current head. Evidence: git diff --check passed; Ollama retry policy tests passed (9 passed, 2 skipped); ruff check and format passed for touched files.