fix(aws-cdk): init template imports not following best practices to use aws-cdk-lib/core

[mrgrain]

Follows CDK best practices by using specific imports from aws-cdk-lib/core instead of importing the entire aws-cdk-lib package.

Affects all JavaScript and TypeScript templates across app, sample-app, and lib init types.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.04%. Comparing base (3d7b09b) to head (8576016).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #916      +/-   ##
==========================================
- Coverage   83.29%   83.04%   -0.26%     
==========================================
  Files          71       71              
  Lines       10401    10401              
  Branches     1311     1305       -6     
==========================================
- Hits         8664     8637      -27     
- Misses       1698     1725      +27     
  Partials       39       39              

Flag	Coverage Δ
suite.unit	83.04% <ø> (-0.26%)	⬇️

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