Refactor upload changes handling

[varmar05]

• move relevant validations into upload schema
• use upload schema only in push init while project file object is used for actual file manipulations
• remove version context and redundant dataclasses for upload schema

[coveralls]

Pull Request Test Coverage Report for Build 15702878345

Details

• 177 of 187 (94.65%) changed or added relevant lines in 10 files are covered.
• 4 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.02%) to 91.683%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
server/mergin/sync/commands.py	0	1	0.0%
server/mergin/sync/files.py	67	71	94.37%
server/mergin/sync/public_api_controller.py	79	84	94.05%

Files with Coverage Reduction	New Missed Lines	%
server/mergin/sync/public_api_controller.py	2	91.31%
server/mergin/sync/utils.py	2	84.08%

Totals
Change from base Build 15629180988:	0.02%
Covered Lines:	7165
Relevant Lines:	7815

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💛 - Coveralls

[MarcelGeo]

Looks nice, I am happy to get rid of version from changes.