Support ILIKE in the expression evaluator

[rishitesh]

Closes #2.

ILIKE was already parsed (from_substrait.cpp sets ignore_case on like_expression, and it round-trips through RPC serialization), but evaluate_expressions threw "Unsupported scalar function" when evaluating it.

Changes

• src/executor/eval.cpp: in the like case, when ignore_case() is set, lowercase the input column, the pattern, and the escape character with cudf::strings::to_lower, then reuse the existing LIKE paths (gqe::like shift-and kernel and the cudf::strings::like fallback). Pattern and escape char are lowered through the same cuDF kernel as the column so their case mappings agree, including for non-ASCII input. % and _ have no case, so the pattern structure is preserved.
• test/executor/eval_expressions_test.cpp: 6 new tests — basic mixed-case matching, _/% wildcards, nullable input, escape characters, UTF-8 (Ärger), and a control test that plain LIKE remains case-sensitive. All run through both execution paths via the existing parameterized suite (filter_use_like_shift_and false/true).

Testing

On an L4 (sm_89), Release build:

• ctest -R eval_expressions passes; the 12 new parameterized cases all pass.
• Full ctest shows no regressions vs main (the cupti_test NVTX case and memory_resource failures reproduce identically on unmodified main in my container environment).
• End-to-end through gqe_node_manager + gqe-cli: ILIKE queries against a mixed-case Parquet table return the expected rows, cross-checked against a Python reference.

One note from e2e testing: patterns not anchored by % (e.g. ILIKE 'w_dget') return incorrect results on the shift-and path — but this reproduces with plain LIKE on main as well, so it's a pre-existing kernel issue rather than something introduced here — filed as #4 with the repro and root cause.