fix: enforce exact name match in get_collection

[kailashv2]

Summary

Fixes #7063

get_collection() was returning a collection even when the requested
name didn't exactly match. For example, querying colls would return
coll if it existed.

Root Cause

The sysdb query uses a partial/prefix match internally. The frontend
never verified that the returned collection's name exactly matched the
requested name.

Fix

Added an exact name check after fetching from sysdb:

• If the returned collection name matches exactly → return it
• If not → return NotFound error

Testing

• Existing tests pass
• Manual test: querying colls when only coll exists now returns 404

[github-actions]

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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?
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• Are there any potential impacts on other parts of the system or backward compatibility?
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Quality

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