build(deps-dev): bump typescript from 5.9.3 to 6.0.3 (#315)

* build(deps-dev): bump typescript from 5.9.3 to 6.0.3

Bumps [typescript](https://github.com/microsoft/TypeScript) from 5.9.3 to 6.0.3.
- [Commits](microsoft/TypeScript@v5.9.3...v6.0.3)

---
updated-dependencies:
- dependency-name: typescript
  dependency-version: 6.0.3
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

* fix(ts): explicit types in tsconfig and bump @types/node to 25.6.0

TypeScript 6.0 no longer auto-loads @types/* by default with this
project's tsconfig setup, so Node and Mocha globals (Buffer, process,
__dirname, describe, it, ...) became unresolved. Pin "types" to
["node", "mocha"] so the compiler picks them up explicitly.

Also bumps @types/node from 25.5.2 to 25.6.0, superseding #314.

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Attila Szegedi <attila.szegedi@datadoghq.com>

Author: dependabot[bot]