fix: correctly handle ESCAPE character in LIKE clause (#1978)

[imsanupm]

Description

Fixes #1978

LIKE clause with backslash \ as ESCAPE character returned no results
instead of correctly filtering rows.

Root Cause

Two bugs in alasql.utils.like in src/15utility.js:

1. Cache key didn't include escape character — when two queries
   used the same pattern but different escape characters, the wrong
   cached regex was reused, giving incorrect results.

2. Backslash as escape broke regex — when \ was used as escape,
   the next character was appended as '\' + nextChar which produced
   a broken regex pattern.

Changes

• src/15utility.js — fixed cache key to include escape character,
  and used proper regex escaping for the literal character after escape

Tests

• 5 new regression tests all passing
• All 2454 existing tests still passing

Verified Scenarios

• ^ as ESCAPE works correctly ✅
• \ as ESCAPE now works correctly ✅
• OR condition with ESCAPE on two columns ✅
• Same pattern with different escape chars uses separate cache entries ✅

[mathiasrw]

We are fixing #1978

How come we create a test file for #1216 and #1953?

[mathiasrw]

Please make a test file named test/test1978.js that will detect if we accidently reintroduces this problem.

[mathiasrw]

@imsanupm are you still on this?