fix(toolkit-lib): warn on empty change sets for unsuccessful stacks

[proton0210]

Summary

• Warn with the stack name and status when an empty change set leaves a stack outside a successful deployment state.
• Suppress the misleading force-deployment claim that all resources are up to date in that case.
• Preserve the no-op result, exit-code behavior, and change-set cleanup. This implements the warning-only first step suggested in cdk deploy reports "(no changes)" and exits 0 while the stack is still in UPDATE_FAILED #1972; it does not change failure exit codes or recovery behavior.

Related to #1972.

Validation

• Toolkit library and test TypeScript compilation passed.
• Deployment stack suite: 100 tests and 1 snapshot passed, including six new cases covering UPDATE_FAILED with/without force, all three successful statuses, and no-execute cleanup after rollback.
• Scoped ESLint and git diff --check passed.
• Three audit passes covered scope/backward compatibility, status and cleanup edge cases, and the final diff/regression suite.
• No live AWS deployment was performed; the regression tests use the existing fake CloudFormation implementation.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.00%. Comparing base (13877dc) to head (4ec6593).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2029      +/-   ##
==========================================
+ Coverage   91.96%   92.00%   +0.03%     
==========================================
  Files          82       82              
  Lines       13138    13138              
  Branches     1864     1867       +3     
==========================================
+ Hits        12083    12087       +4     
+ Misses       1017     1013       -4     
  Partials       38       38              

Flag	Coverage Δ
suite.unit	92.00% <ø> (+0.03%)	⬆️

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