Remove misleading LanceDB naming

[FANNG1]

Summary

• Rename the internal Lance scan operator and Python factory helpers away from LanceDB terminology.
• Update docstrings and examples to describe Lance datasets instead of LanceDB tables/client usage.
• Move tests from tests/io/lancedb to tests/io/lance and rename affected test files, classes, functions, imports, and explain-output assertions.

Closes #33.

Checks

• make check-format passed.
• make lint passed.
• uv run pytest tests/io/lance -v reported 278 passed, 5 skipped, 2 xfailed, 2 xpassed, but the process exited with code 139 after printing the summary.
• uv run pytest -p no:benchmark tests/io/lance/test_lance_count_pushdown_coverage.py tests/io/lance/test_lance_factory_function.py tests/io/lance/test_lance_point_lookup.py tests/io/lance/test_lance_reads.py -v reported 68 passed, 2 skipped, 2 xpassed, but also exited with code 139 after printing the summary.
• make typecheck failed on existing mypy issues across tests and a few existing Lance typing mismatches; no failures appeared specific to the naming change.

Notes

• The only remaining lancedb text from rg -i "lancedb|lance db" is the factual upstream URL https://github.com/lancedb/lance/....

[FANNG1]

@rchowell , could you help to review this PR, thanks!

[rchowell]

Hey @FANNG1 - thanks for the PR!

Renaming classes would be breaking change, could you please re-export the existing public class names with a deprecation notice?

Thank you.

[FANNG1]

Thanks for the review. I updated the PR to keep the existing LanceDB-named scan symbols as deprecated compatibility aliases, while the new Lance names remain the preferred ones.

Specifically, I kept these old names which in https://github.com/Eventual-Inc/Daft/blob/62cb100858c43a5a92f3bac33d6ecdcefbfa8f8d/daft/io/lance/lance_scan.py#L10-L12:

• LanceDBScanOperator -> LanceScanOperator
• _lancedb_table_factory_function -> _lance_table_factory_function
• _lancedb_count_result_function -> _lance_count_result_function

Each alias now emits a DeprecationWarning and forwards to the new Lance-named implementation. I also added regression coverage for the deprecated aliases.

[FANNG1]

@rchowell This PR has now been rebased onto the latest main and the conflicts have been resolved. Given the current state of the codebase, do you think this naming cleanup is still worth moving forward with, or would you prefer that we close the PR?