Add isClean entity state checks

[elpete]

Closes #50

Issue review

Recommendation: 10/10 — implement. isClean makes the inverse state check readable and avoids repeated negation throughout consuming applications. Supporting one alias or column is especially useful for conditional work tied to a specific field. This is additive and low risk.

Implementation

• adds isClean() for whole-entity state
• adds isClean(attribute) for a Quick alias or physical column
• uses the same case-sensitive attribute hashing semantics as isDirty
• validates unknown attributes through the normal Quick error path

Test-first evidence

The public regression initially errored with QuickMissingMethod. It now covers a fully clean entity, clean alias and physical-column checks, whole-entity dirtiness after a change, the changed field becoming unclean, and an unrelated field remaining clean.

Review note

This PR is independently mergeable against next. PR #343 adds the complementary optional-attribute support to isDirty; if both are merged, a small follow-up refactor could share their per-attribute comparison helper, but neither PR depends on the other.

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.