Allow isDirty checks for one attribute

[elpete]

Closes #51

Issue review

Recommendation: 10/10 — implement. Callers frequently need to decide whether one field changed for auditing, conditional side effects, or targeted validation. Requiring a whole-entity dirty result forces manual comparison against internal state. This is a small, backward-compatible API improvement with little downside.

Implementation

• adds an optional attribute argument to isDirty
• accepts either Quick aliases (firstName) or physical columns (first_name)
• uses the same case-sensitive hashing semantics as whole-entity dirtiness
• retains the cached whole-entity hash path when no attribute is supplied
• rejects unknown attributes through Quick’s normal attribute validation

Test-first evidence

The first regression showed that CFML accepted the extra argument but the old implementation ignored it: after changing username, isDirty("firstName") incorrectly returned true. The test now covers clean attributes, dirty aliases, dirty physical columns, reverting one field, and whole-entity state.

Validation

• focused IsDirtySpec: 2 passed, 0 failed, 0 errors
• full Lucee 6 suite: 496 passed, 0 failed, 0 errors, 3 skipped
• box run-script format
• git diff --check

Uses qb@14.0.0-beta.3.