refactor(toolkit-lib): standardize confirmation requests to use ConfirmationRequest interface

[mrgrain]

This PR standardizes user confirmation flows across the CDK CLI by migrating from ad-hoc promptly.confirm usage to the structured ConfirmationRequest interface.

These are the changes as suggested here: #826 (review)

Changes

• Convert CDK_TOOLKIT_I8910: Changed from DataRequest to ConfirmationRequest for refactor confirmation
• Standardize destroy flow: Replace promptly.confirm with IO.CDK_TOOLKIT_I7010 message
• Standardize deploy flow: Update askUserConfirmation to use ActionLessRequest<ConfirmationRequest> pattern
• Clean up test infrastructure: Remove deprecated markTesting function and TESTING variable
• Update tests: Replace promptly mocks with requestSpy for consistency

Benefits

• Consistent user interaction patterns across all CLI commands
• Better testability through standardized mocking
• Improved error handling and TTY detection through the IO system
• Cleaner separation of concerns between UI logic and business logic

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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

❌ Patch coverage is 38.23529% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.95%. Comparing base (09c0061) to head (ad5f7e7).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/aws-cdk/lib/cli/cdk-toolkit.ts	38.23%	21 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #904      +/-   ##
==========================================
- Coverage   83.69%   82.95%   -0.75%     
==========================================
  Files          65       65              
  Lines        9558     9546      -12     
  Branches     1135     1117      -18     
==========================================
- Hits         8000     7919      -81     
- Misses       1535     1605      +70     
+ Partials       23       22       -1     

Flag	Coverage Δ
suite.unit	82.95% <38.23%> (-0.75%)	⬇️

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