chore: migrate to yarn berry

[mrgrain]

This migrates the monorepo from Yarn Classic to Yarn Berry by enabling the yarnBerry projen option and re-synthesizing the project.

Yarn Classic (v1) has been in maintenance mode for years and Yarn Berry provides better dependency resolution, improved performance, and stricter dependency management. This is a necessary step to keep the toolchain current and benefit from ongoing improvements in the Yarn ecosystem.

The manual changes in .projenrc.ts enable the yarnBerry: true flag on the monorepo and introduce a consistentVersions configuration. The consistent versions list ensures that shared tooling dependencies like typescript, eslint and its plugins, prettier, and jest-junit are pinned to the same version across all packages in the monorepo. This avoids subtle issues from version mismatches between packages, which Yarn Berry is more strict about enforcing. A few dependencies are marked with @todo comments where consistent versioning still needs to be worked out.

Additionally, ts-node is added as a dev dependency to the aws-cdk CLI package. Yarn Berry resolves peer dependencies more strictly than Classic, so transitive availability of ts-node can no longer be relied upon and it needs to be declared explicitly.

All other file changes (workflows, package.json files, lockfile, .yarnrc.yml, yarn.config.cjs, etc.) are auto-generated by running projen synthesis after these manual changes.

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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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.28%. Comparing base (c716037) to head (27ef2c3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1326      +/-   ##
==========================================
+ Coverage   88.20%   88.28%   +0.07%     
==========================================
  Files          73       73              
  Lines       10386    10386              
  Branches     1409     1415       +6     
==========================================
+ Hits         9161     9169       +8     
+ Misses       1198     1190       -8     
  Partials       27       27              

Flag	Coverage Δ
suite.unit	88.28% <ø> (+0.07%)	⬆️

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