Touch only configured timestamp fields

[elpete]

Closes #53

Issue review

Recommendation: 8/10 — touch is a useful entity-level operation, but it must not accidentally persist unrelated dirty state.

Implementation

• adds timestampFields(), defaulting to [ "modifiedDate" ], so entities can override the timestamp attributes they use
• makes touch() restore the entity to its last clean state before assigning timestamps
• uses one timestamp value for every configured field and then saves normally, preserving Quick lifecycle behavior
• keeps query execution options available through touch( options = {} )

Regression coverage

• proves a dirty non-timestamp attribute is restored in memory and is not persisted
• proves the default modified timestamp is updated and the entity is clean afterward
• proves an entity override of timestampFields() controls which timestamp is touched

Validation

• focused Lucee 6 SaveSpec: 20 passed, 0 failed, 0 errors
• formatting check passed
• git diff --check passed

Uses qb@14.0.0-beta.3 and targets next.