Remove oj dependency to restore JRuby support

[najibna]

Description

Fixes #1461

oj is an unused native C-extension dependency. It cannot be installed on JRuby and is not called at runtime, so it only blocks JRuby users.

This PR removes it from the gemspec, requires, lockfile, and generated RBI files.

How has this been tested?

• bundle exec rake test — 342 runs, 0 failures
• bundle exec srb tc — no errors

Checklist:

• My commit message follow the pattern described in here
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works.
• I have updated the project documentation.
• I have added a changelog line.

[najibna]

I have signed the CLA!

[najibna]

Ready for review.

CLA is signed. Tests and srb tc pass. Changelog is updated. No docs change needed for this dependency removal.