build: emit sourcemaps for CJS and ESM builds

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Summary

• Enables sourceMap, declarationMap, and inlineSources in tsconfig.base.json, so both CJS and ESM builds emit .js.map / .d.ts.map files with TypeScript source embedded.
• Maps ship inside npm pack automatically — files: ["dist"] already covers them; no files or .npmignore change needed.
• Tarball unpacked size grows from ~78 KB to ~142 KB (gzipped: 28 KB) — driven by inlined sources.

Why inlineSources

We publish only dist/ (not src/), so external sources paths in the .map files would be dangling on consumers' machines. Inlining the TS source into sourcesContent is the standard fix for libraries and makes sourcemaps self-contained.

Verification

• Clean rebuild produces .js.map + .d.ts.map for every .js / .d.ts in both dist/cjs/ and dist/esm/.
• Each emitted .js ends with //# sourceMappingURL=...map.
• sourcesContent[0] in the map files contains the full TS source.
• npm pack --dry-run lists 16 map files in the tarball.
• With node --enable-source-maps, a thrown error from a built CJS/ESM entrypoint resolves to src/NtpTimeSync.ts:<line> (verified locally).
• CJS and ESM integration tests still pass; examples/example.js still runs.

Test plan

• CI green across Node 20/22/24/25 matrix (build + CJS + ESM integration).
• Deno matrix still green.
• Prettier workflow still green.

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