Scope test:unit to tests/unit and normalize placeholder scripts (Fixes #5643)

[ssmurfgg04-gif]

What

Following the plan in #5643:

• test:unit is now vitest --run tests/unit in every package that had the bare vitest --run (commons, batch, jmespath, kafka, testing, validation), so a local npm run test:unit no longer pulls in the e2e suites that need AWS credentials.
• Placeholder strings for test:e2e and test:unit:types are normalized to a single form, echo 'Not Implemented', across packages/*.
• vitest run is normalized to vitest --run, and the test:unit:types flag order is unified to vitest --run tests/types --typecheck.

Why

As described in #5643: running unit tests locally in batch (and five other packages) executes the SQS e2e suite, which fails or hangs without AWS credentials. The placeholder drift also defeats grepping for which packages lack a suite.

Verification

• Confirmed each touched package has a tests/unit directory, so the scoped path resolves.
• Diff is scripts-only, package.json contents otherwise untouched.
• I left CODING_STANDARDS.md alone to keep this reviewable; happy to add the canonical forms there in a follow-up if preferred.

Fixes #5643

[powertools-for-aws-oss-automation]

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[powertools-for-aws-oss-automation]

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[svozza]

Please fix this PR to follow our repo conventions. There is a create-issue skill you can point your agent to that will do this.

[dreamorosi]

Thank you for taking the time to contribute! We've decided to handle this one as maintainers since it touches conventions we're standardizing across the repo, and it's now addressed in #5653. Closing this in favor of that PR — we'd be happy to see you pick up another issue.

[ssmurfgg04-gif]

Fair enough, repo conventions win. Thanks for folding it into #5653 and for the invite, I will go through the open issues and pick up another one.