[itzKLAUS]

Enable full TypeScript strict checking in place of strictNullChecks, as requested in #352.

Closes #352

Add explicit types for the nullish helper, encoded array pairs and dynamically indexed test examples. Copy sanitized message properties through a generic key so their value types remain correlated. Narrow the caught decryption error's optional message while preserving the existing error-message checks. No strict options are disabled, and no new any annotations or suppression comments are added.

Validation on Windows / Node 24.19.0 with the pinned Yarn 4.16.0 and TypeScript 4.8.4:

• yarn install --immutable, yarn build and yarn lint passed.
• The source suite passed: 1,391 tests and 712 unchanged snapshots across six suites, with the repository coverage thresholds met.
• yarn test --runInBand also passed after the build (it runs both source tests and emitted tests under dist, so its 2,782-test count includes duplicates).
• Enabling strict checking alone initially produced compiler errors; the final patch compiles with strict: true.

Local checkout line endings were normalized to LF for lint, and a local yarn command shim delegated to Corepack. Neither is included in the diff. The existing dependency peer warnings remain; dependencies and the lockfile were not changed. Node 22/26 and hosted CI were not run locally.

The broader module-template PR #351 still retains strictNullChecks; this change addresses the strict setting independently.

[FrederikBolding]

Closing in favor of moving to core repo. Thanks for the contribution!