fix(field): #1370 isDirty flag reset on initialValue

[majumdersubhanu]

Connection with issue(s)

Close #1370

Solution description

• Reset isDirty flag if the current value in a form field matches the defined initial value.
• Corresponding tests

Screenshots or Videos

To Do

• Read contributing guide
• Check the original issue to confirm it is fully satisfied
• Add solution description to help guide reviewers
• Add unit test to verify new or fixed behaviour
• If apply, add documentation to code properties and package readme

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.82%. Comparing base (38a24f6) to head (3afd6f2).

Files with missing lines	Patch %	Lines
lib/src/form_builder_field.dart	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1507      +/-   ##
==========================================
- Coverage   90.85%   90.82%   -0.04%     
==========================================
  Files          21       21              
  Lines         853      861       +8     
==========================================
+ Hits          775      782       +7     
- Misses         78       79       +1     

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[Copilot]

Pull request overview

Fixes reported isDirty behavior so a field (and thus the form) is no longer considered dirty when its current value matches the configured initialValue, and prevents reset() from triggering recursive onChanged/reset() flows.

Changes:

• Update FormBuilderFieldState dirty tracking to derive isDirty from value vs initialValue.
• Adjust reset() ordering to clear dirty before emitting change notifications.
• Add widget tests covering “return to initial value” and recursion/overflow scenarios.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
lib/src/form_builder_field.dart	Changes dirty calculation and reorders reset() to avoid re-entrant dirty state during callbacks.
test/src/form_builder_test.dart	Adds a form-level test verifying FormBuilderState.isDirty clears when user returns to initial value.
test/src/form_builder_field_test.dart	Adds field-level tests for isDirty clearing and a regression test intended to cover reset recursion behavior.

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[majumdersubhanu]

@deandreamatias could you please take a look at this PR?

[deandreamatias]

I need a time to take a look deeply on this, because can affect other parts of ecosystem.