chore: make content_type type optional

[fedeerbes]

🔘 PR Type

What kind of change does this PR introduce?

• [ ] Bugfix
• [ ] Enhancement
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation content changes
• [ ] Other... Please describe:

📜 Background

Provide a brief explanation of why this pull request is needed. Include the problem you are solving or the functionality you are adding. Reference any related issues.

Issue Link: #[issue_number] Context Link (if applicable):

🔄 Changes

Does this PR introduce a breaking change?

• [ ] Yes, Incompatible API changes
• [ ] No, Adds functionality (backwards compatible)
• [ ] No, Bug fixes (backwards compatible)

Changes:

• What has been modified, added, or removed
• Which are breaking changes

Impact:

• How it improves performance, fixes bugs, adds functionality, etc.
• Impact on downstream apps, link to issues or PRs for migration
• What to test

🖼 Screenshot / 📹 Video

✅ Review checklist

Please ensure the following are true before merging:

• [ ] Code Style is consistent with the project guidelines.
• [ ] Code is readable and well-commented.
• [ ] No unnecessary or debugging code has been added.
• [ ] Security considerations have been taken into account.
• [ ] The change has been manually tested and works as expected.
• [ ] Breaking changes and their impacts have been considered and documented.
• [ ] Code does not introduce new technical debt or issues.

[github-actions[bot]]

Test this PR with npm i --save-exact @secretkeylabs/xverse-core@9.0.0-772f9ec