feat: add raw log ingestion helpers

[dcfocus]

Summary

• add Python helpers for raw interaction-log ingestion from mapped row iterables, JSONL, and OpenAI-style messages
• preserve raw provenance under metadata and allow caller-supplied run_id / created_at on local add, add_many, and upsert paths
• add focused tests for provenance mapping, streaming JSONL batches, idempotent upsert ingestion, and chat message ingestion

Testing

• cargo fmt --manifest-path python/Cargo.toml
• cargo fmt --manifest-path python/Cargo.toml -- --check
• env PROTOC=/home/user/data-iq/.venv/lib/python3.12/site-packages/torch/bin/protoc PROTOC_INCLUDE=/home/user/data-iq/.venv/lib/python3.12/site-packages/grpc_tools/_proto uv run --project python --extra dev ruff check python/python/lance_context/api.py python/tests/test_ingestion.py
• env PROTOC=/home/user/data-iq/.venv/lib/python3.12/site-packages/torch/bin/protoc PROTOC_INCLUDE=/home/user/data-iq/.venv/lib/python3.12/site-packages/grpc_tools/_proto uv run --project python --extra tests pytest python/tests/test_ingestion.py python/tests/test_add_many.py python/tests/test_state_metadata.py python/tests/test_external_id.py
• env PROTOC=/home/user/data-iq/.venv/lib/python3.12/site-packages/torch/bin/protoc PROTOC_INCLUDE=/home/user/data-iq/.venv/lib/python3.12/site-packages/grpc_tools/_proto uv run --project python --extra dev pyright python/python/lance_context/api.py python/python/lance_context/init.py
• git diff --check

Notes

• The repo PR helper script was attempted but is stale for the current layout: it fails on missing manifest path rust/lance-context/Cargo.toml before running checks.
• Full-repo pyright still reports existing unrelated errors in examples/tests, so this PR uses a scoped pyright check for the touched public API files.

Closes #97