feat: add set alias to KaiselNavigator

[awishere]

Closes #73.

Adds set(...) as an assignment-oriented alias for restoreStack(...) on
the type-erased KaiselNavigator API.

The alias delegates to the existing restoration path, preserving route type
validation, guards, and history behavior. The strongly typed
KaiselRouter<R>.set(List<R>) API remains unchanged.

A regression test covers assigning a stack through a value statically typed
as KaiselNavigator.

Testing:

• dart format --output=none --set-exit-if-changed .
• dart analyze packages/kaisel_core packages/kaisel packages/kaisel_devtools packages/kaisel_lint/lib packages/kaisel_lint/test
• dart test in packages/kaisel_core
• flutter test --no-pub --coverage test/.test_optimizer.dart in packages/kaisel
• flutter test --no-pub --coverage test/.test_optimizer.dart in packages/kaisel_devtools
• dart test --coverage=coverage in packages/kaisel_lint

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (55ee3ec) to head (dc0f119).

Additional details and impacted files

@@            Coverage Diff            @@
##               dev       #75   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           42        42           
  Lines         2322      2323    +1     
=========================================
+ Hits          2322      2323    +1     

Flag	Coverage Δ
kaisel	100.00% <100.00%> (ø)
kaisel_core	100.00% <100.00%> (ø)
kaisel_devtools	100.00% <100.00%> (ø)
kaisel_lint	100.00% <100.00%> (ø)

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