refactor: make BuiltInContainer public

[payam-zahedi]

fixes: #228

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.04%. Comparing base (670035c) to head (53322ba).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #240      +/-   ##
==========================================
+ Coverage   74.43%   77.04%   +2.61%     
==========================================
  Files          32       33       +1     
  Lines         927      928       +1     
==========================================
+ Hits          690      715      +25     
+ Misses        237      213      -24     

Flag	Coverage Δ
flutter	77.04% <100.00%> (+2.61%)	⬆️

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[Copilot]

Pull request overview

Refactors the built-in toast wrapper behavior into a standalone, publicly exported BuiltInContainer so custom toasts can reuse built-in interactions (hover pause, click handling, drag-to-dismiss), aligning with the goal in issue #228.

Changes:

• Extracts _BuiltInContainer / _FadeDismissible from BuiltInBuilder into a new BuiltInContainer widget and exports it from the package.
• Updates BuiltInBuilder to use BuiltInContainer and adjusts public exports accordingly.
• Replaces the previous BuiltInBuilder cursor test with a new, broader BuiltInContainer test suite (margin, hover pause, tap, cursor, drag-to-dismiss).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
test/src/built_in/built_in_container_test.dart	New widget tests covering BuiltInContainer behaviors (padding, hover pause, tap, cursor, drag-to-dismiss).
test/src/built_in/built_in_builder_test.dart	Removes the older BuiltInBuilder-focused cursor test file.
lib/toastification.dart	Exports BuiltInContainer publicly (hiding only test keys) and adjusts BuiltInBuilder export hides.
lib/src/core/toastification.dart	Updates showCustom API surface (removes dismissDirection parameter).
lib/src/built_in/widget/built_in_container.dart	Adds new public BuiltInContainer implementation (including drag-to-dismiss wrapper).
lib/src/built_in/built_in_builder.dart	Swaps internal container usage to the new exported BuiltInContainer and removes embedded container code.

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