[ABA-32] test: repro for missing LIKE ESCAPE plumbing (vortex-array + vortex-datafusion)

[abnobdoss]

Summary

• Adds two #[ignore]'d regression tests that document the gap described in ABA-32: LikeOptions has no escape_char field, making SQL LIKE … ESCAPE semantics unrepresentable in the Vortex expression layer.
• vortex-array (scalar_fn/fns/like/mod.rs): issue_aba32_like_options_supports_escape_char — asserts LikeOptions Debug output contains escape_char; fails on develop.
• vortex-datafusion (convert/exprs.rs): issue_aba32_datafusion_conversion_preserves_like_escape_char — converts a DataFusion LikeExpr via DefaultExpressionConvertor and asserts the resulting LikeOptions exposes escape information; fails on develop.

This is a REPRO-ONLY PR — no production code is changed.

Gap analysis

LikeOptions (vortex-array) only carries negated and case_insensitive. There is no escape_char: Option<char> field. The proto LikeOpts message is equally absent. As a consequence:

1. Non-DataFusion frontends cannot express any escape char.
2. The DataFusion physical LikeExpr (DF 53) also has no escape_char field; the logical layer drops it during create_physical_expr. So even if Vortex added the field, the DataFusion conversion path currently has nothing to plumb through.

Relation to PR vortex-data#8038

PR vortex-data#8038 ("Fallback from fsst specialised like expression if there are escape characters in the like string") adds a pattern-byte inspection (pattern.contains(&b'\\')) in the FSST DFA fast-path so it safely bails out when the pattern contains a backslash. This is a correctness guard for the fast path, not an addition of escape-char support. The schema gap (missing escape_char on LikeOptions) is confirmed to still exist on develop.

Open questions

• Should LikeOptions gain escape_char: Option<char> now (with None meaning the SQL default \), or wait until DataFusion exposes the field on the physical LikeExpr?
• Once added, the FSST fast-path bailout in dfa/mod.rs should be generalised to check options.escape_char (defaulting to Some('\\')) rather than scanning pattern bytes for \.
• Proto schema (vortex-proto/proto/expr.proto → LikeOpts) will need a new optional field and a migration note.

🤖 Generated with Claude Code

Linear: https://linear.app/abanoubdoss/issue/ABA-32