Added to_version as latest project version to delta reponse + another response updates

[MarcelGeo]

When pulling transaction starts in clients, we need to know in which version s client operating to perform successfull project info and finish of pull.

• to_version key added to response
• diff.path changed to diff.id in response as this path is abstract and for clients it's not path, just some file somewhere - it could be also name

Other:

• improve handling of empty delta if since equals to to (or latest project version) -> returns items: [], bacuase clients will ping this endpoint everytime when somebody will try to pull.

[Copilot]

Pull request overview

This PR adds a to_version field to the project delta API response and modifies the validation logic to allow queries where since equals to (previously returned a 400 error). This change enables clients to poll the delta endpoint without errors when no changes have occurred since their last sync.

Key Changes:

• Added to_version field to delta response schema to indicate the target version
• Modified validation to allow since == to queries, returning an empty items list instead of an error
• Updated error messages to be more descriptive and contextually appropriate

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
server/mergin/sync/public_api_v2_controller.py	Updated validation logic to allow since == to, refactored error messages, and added to_version to response
server/mergin/sync/files.py	Added to_version field to DeltaChangeRespSchema with required=True
server/mergin/sync/public_api_v2.yaml	Added to_version property to ProjectDeltaResponse schema and minor formatting fix
server/mergin/tests/test_public_api_v2.py	Added test assertions for to_version field, new test for since==to case, removed old test that expected 400 for same versions

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[coveralls]

Pull Request Test Coverage Report for Build 20166872065

Details

• 35 of 35 (100.0%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.009%) to 94.539%

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Files with Coverage Reduction	New Missed Lines	%
server/mergin/sync/public_api_v2_controller.py	1	91.14%

Totals
Change from base Build 19732530660:	0.009%
Covered Lines:	8656
Relevant Lines:	9156

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💛 - Coveralls

[varmar05]

update also docstring