feat(core): add Levenshtein-based suggestions to not-found errors in schema

[HemantSudarshan]

What

Closes #5642 (incrementally)

Enhances "column not found" and "field not found" error messages in Schema to suggest the closest matching field name using Levenshtein distance.

Before:
LanceError(Schema): Column vectr does not exist

After:
LanceError(Schema): Column vectr does not exist. Did you mean 'vector'?

Changes

Single file modified: lance-core/src/datatypes/schema.rs

• Added levenshtein_distance() — standard edit distance with two-row DP optimization
• Added suggest_field() — finds closest field name (threshold: edit distance ≤ 1/3 of the longer name's length)
• Enhanced 3 error sites:
  • FieldRef::into_id — "Field 'X' not found in schema"
  • Schema::do_project — "Column X does not exist"
  • Schema::project_by_schema — "Field X not found"

Design Decisions

• No new dependencies — implemented Levenshtein inline rather than adding strsim crate
• No new error variants — enhanced existing Error::InvalidInput and Error::Schema message strings
• 1/3 threshold — per issue guidance: suggestions only appear when fewer than 1/3 of characters need to change, preventing unhelpful suggestions for completely unrelated names
• Incremental scope — this PR covers schema.rs only; additional error sites (scanner, projection, etc.) can follow

Testing

Added 4 tests:

• test_levenshtein_distance — 11 assertions covering identical, empty, single-edit, multi-edit, and completely different strings
• test_suggest_field — 6 assertions: close match, no match, exact match rejection, empty list, short names
• test_suggest_field_edge_cases — 2 assertions: all-different short names, picks-closest-among-multiple
• test_project_with_suggestion — integration test: verifies Schema::project includes suggestion for typo, and omits it for completely wrong names

[codecov]

Codecov Report

❌ Patch coverage is 90.78947% with 14 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rust/lance-core/src/error.rs	69.23%	2 Missing and 6 partials ⚠️
rust/lance-core/src/levenshtein.rs	94.36%	4 Missing ⚠️
rust/lance-core/src/datatypes/schema.rs	97.91%	1 Missing ⚠️
rust/lance/src/dataset/metadata.rs	85.71%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[wjones127]

Thanks for making a PR. This is a good start, but it misses a key requirement from the original issue:

I would recommend implementing the suggestion in the Display implementation instead of when creating the error. That way, we don't perform a complex calculation for the suggestion when the error might be expected and immediately handled.

Here is an example of how that might work: https://github.com/lance-format/lance/pull/5830/changes#diff-d8784e118b0c126058a9c40901117a537eb97065e1def0ddb94ec47ce5a2a9aeR16-R44

I think I'd prefer to create a new error variant to accomplish this, rather than re-using existing variants.

[wjones127]

This is great work! I will merge once tests are passing.