feature: add ilike support

[jja725]

---

feat: add ILIKE case-insensitive pattern matching

Implements ILIKE operator that works like LIKE but ignores case.
Leverages DataFusion's case_insensitive flag on Like expressions.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 84.61538% with 16 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...t/lance-graph/src/datafusion_planner/expression.rs	83.92%	9 Missing ⚠️
rust/lance-graph/src/parser.rs	89.13%	5 Missing ⚠️
rust/lance-graph/src/semantic.rs	0.00%	2 Missing ⚠️

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[ChunxuTang]

lgtm. just very minor comments.