[CLN] fix minor typos

[CasiCode]

Description of changes

Fixed some minuscule typos in rust/types/src/api_types.rs.

Test plan

No tests needed.

Documentation Changes

No documentation changes needed.

[propel-code-bot]

This PR corrects minor typographical errors in the error messages of several enum variants in rust/types/src/api_types.rs, specifically changing 'does not exists' to the grammatically correct 'does not exist'. No behavioral or logic changes are introduced.

This summary was automatically generated by @propel-code-bot

[github-actions]

Reviewer Checklist

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Testing, Bugs, Errors, Logs, Documentation

• Can you think of any use case in which the code does not behave as intended? Have they been tested?
• Can you think of any inputs or external events that could break the code? Is user input validated and safe? Have they been tested?
• If appropriate, are there adequate property based tests?
• If appropriate, are there adequate unit tests?
• Should any logging, debugging, tracing information be added or removed?
• Are error messages user-friendly?
• Have all documentation changes needed been made?
• Have all non-obvious changes been commented?

System Compatibility

• Are there any potential impacts on other parts of the system or backward compatibility?
• Does this change intersect with any items on our roadmap, and if so, is there a plan for fitting them together?

Quality

• Is this code of a unexpectedly high quality (Readability, Modularity, Intuitiveness)

[HammadB]

thank you!