feat: add improvements in Typescript API

[g4rcez]

Checklist

• [x] run npm run test and npm run benchmark
• [x] tests and/or benchmarks are included
• [ ] documentation is changed or added
• [ ] commit message and code follows the Developer's Certification of Origin and the Code of conduct

Add some utilities for better typing in ObjectSchema.

[aboutlo]

Thank you, @g4rcez, for these improvements! I will let others have a look, too, but LGTM.

[coveralls]

Pull Request Test Coverage Report for Build 3209062838

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 3177673423:	0.0%
Covered Lines:	403
Relevant Lines:	403

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 3273614482

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 3177673423:	0.0%
Covered Lines:	403
Relevant Lines:	403

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💛 - Coveralls