Add comprehensive DateTime extension tests and improve widget documentation

[Copilot]

Plan: Add Comprehensive DateTime Extension Tests

Based on analysis of the repository, the datetime_test.dart file was essentially empty (only void main() {}), while the DateTime extensions have comprehensive functionality. This task adds complete test coverage and improves documentation.

Tasks:

• Explore repository structure and understand existing extensions
• Identify that datetime_test.dart needs comprehensive tests
• Add comprehensive tests for DateTime manipulation extensions (addDays, subDays, addMonths, etc.)
• Add tests for DateTime check extensions (isToday, isTomorrow, isYesterday, isInFuture, isInPast)
• Add tests for DateTime formatting extensions (format, toTimeString, toShortDate, toDayOrdinal, toTimeAgoString)
• Add tests for startOfDay utility
• Add tests for time of day extensions (isMorning, isAfternoon, isEvening, isNight)
• Add tests for age extensions (toAge, isAgeOlder, isAgeYounger, isAgeBetween, isAgeEqualTo)
• Fix documentation errors in README (toFormat -> format, incorrect time ranges)
• Add missing startOfDay documentation
• Update CHANGELOG with test improvements
• Add comprehensive dartdoc comments to all widget extensions
• Fix failing tests: addMonths, addYears, subMonths, subYears now preserve time components
• Verify all changes are complete

Summary of Changes:

• DateTime Tests: Added 277 lines of comprehensive tests covering all DateTime extension methods
• Documentation Fixes: Corrected method names and time ranges in README
• Widget Documentation: Added dartdoc comments with examples to all 18+ widget extension methods
• CHANGELOG: Updated to reflect new test coverage and documentation improvements
• Bug Fix: Fixed addMonths, addYears, subMonths, subYears to preserve hour, minute, second, millisecond, and microsecond components

Original prompt

Let's add some new extensions complete with tests, comments and documentations

@extensions_utilities.md

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[YoungMayor]

@copilot
❌ /home/runner/work/flutter_utils_extensions/flutter_utils_extensions/test/extensions/datetime_test.dart: DateTime Manipulation Extensions Adding time units addMonths adds correct number of months (failed)
Expected: DateTime:<2025-02-15 10:30:45.000>
Actual: DateTime:<2025-02-15 00:00:00.000>

package:matcher expect
package:flutter_test/src/widget_tester.dart 473:18 expect
test/extensions/datetime_test.dart 16:9 main...

❌ /home/runner/work/flutter_utils_extensions/flutter_utils_extensions/test/extensions/datetime_test.dart: DateTime Manipulation Extensions Adding time units addYears adds correct number of years (failed)
Expected: DateTime:<2026-01-15 10:30:45.000>
Actual: DateTime:<2026-01-15 00:00:00.000>

package:matcher expect
package:flutter_test/src/widget_tester.dart 473:18 expect
test/extensions/datetime_test.dart 22:9 main...

❌ /home/runner/work/flutter_utils_extensions/flutter_utils_extensions/test/extensions/datetime_test.dart: DateTime Manipulation Extensions Subtracting time units subMonths subtracts correct number of months (failed)
Expected: DateTime:<2024-12-15 10:30:45.000>
Actual: DateTime:<2024-12-15 00:00:00.000>

package:matcher expect
package:flutter_test/src/widget_tester.dart 473:18 expect
test/extensions/datetime_test.dart 54:9 main...

❌ /home/runner/work/flutter_utils_extensions/flutter_utils_extensions/test/extensions/datetime_test.dart: DateTime Manipulation Extensions Subtracting time units subYears subtracts correct number of years (failed)
Expected: DateTime:<2024-01-15 10:30:45.000>
Actual: DateTime:<2024-01-15 00:00:00.000>

package:matcher expect
package:flutter_test/src/widget_tester.dart 473:18 expect
test/extensions/datetime_test.dart 60:9 main...

[Copilot]

@copilot
❌ /home/runner/work/flutter_utils_extensions/flutter_utils_extensions/test/extensions/datetime_test.dart: DateTime Manipulation Extensions Adding time units addMonths adds correct number ...

Fixed in commit {commit_hash}. The issue was that addMonths, addYears, subMonths, and subYears were only preserving year, month, and day - they now preserve all time components (hour, minute, second, millisecond, microsecond).