refactor: use projen primitives for custom workflow definitions

[mrgrain]

The custom GitHub workflow definitions in projenrc/ hardcode Node.js setup steps and shell commands like yarn workspaces run bump or npx tsx projenrc/publish-to-adc.task.ts. This means that whenever the project's package manager or tooling changes (e.g. migrating from Yarn Classic to Berry), every custom workflow needs to be manually updated to match. Meanwhile, projen-managed workflows already handle this automatically through renderWorkflowSetup() and runTaskCommand().

This refactoring replaces the manual step definitions with projen primitives across all three custom workflow files. In adc-publishing.ts, the hardcoded setup-node and yarn install steps are replaced with renderWorkflowSetup(), and the direct npx tsx invocation is wrapped in a proper publish-to-adc projen task that is then called via runTaskCommand(). In cdk-cli-integ-tests.ts, the same setup replacement is applied, and the hardcoded yarn workspaces run bump and npx projen build commands are replaced with their runTaskCommand() equivalents. In codecov.ts, the manual setup steps are similarly replaced with renderWorkflowSetup().

The regenerated workflow YAML files reflect these changes: actions/setup-node is updated from v4 to v6, the package-manager-cache setting is now explicitly configured, and all task invocations go through npx projen instead of direct tool calls. These are all consequences of using the projen primitives rather than manual changes.

Checklist

• This change contains a major version upgrade for a dependency and I confirm all breaking changes are addressed
  • Release notes for the new version:

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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 88.20%. Comparing base (30d50ce) to head (ff3a1f3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1322   +/-   ##
=======================================
  Coverage   88.19%   88.20%           
=======================================
  Files          73       73           
  Lines       10386    10386           
  Branches     1410     1409    -1     
=======================================
+ Hits         9160     9161    +1     
+ Misses       1199     1198    -1     
  Partials       27       27           

Flag	Coverage Δ
suite.unit	88.20% <ø> (+<0.01%)	⬆️

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