Align Node.js support with the nodejs22.x/nodejs24.x layer (T-17775)

[radike]

AWS Lambda's nodejs20.x runtime is reaching end of life. This aligns the extension's supported Node.js versions with the nodejs22.x/nodejs24.x runtimes (T-17775).

Changes

• package.json — engines.node: >=16.0.0 → >=22.0.0
• CI — test matrix on Node 22 and 24 with fail-fast: false; the job name carries the version
• CI — cache key now uses the matrix version; the previous key referenced env.NODE_VERSION, which was undefined
• CI — new Build step running pnpm run build

Verification

Lint, all 22 tests, and the build pass on clean node:22 and node:24 containers with pnpm@8 and --frozen-lockfile; both versions produce an identical 136,272-byte dist/extension.zip.

Notes

• The first CI run on this branch gets no cache hit on either job — the key changed, which is the intended fix, so both install from scratch once.
• The engines bump is advisory: the repo has no engine-strict=true, so it documents intent without blocking older Node versions at install time.
• @types/node deliberately stays at ^18: bumping it to ^22 resolves Request to node-fetch v3's type instead of the v2 type jest-fetch-mock expects, breaking three suites. That node-fetch v2/v3 cleanup belongs in a separate ticket.

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