Envelopes Serialization Improvements

[philipphofmann]

Description

After crashing the SDK on startup due to corrupted envelope data with #4280, we must ensure this doesn't happen again. This is a meta issue to collect the improvements to achieve that goal. The plan is to increase the test coverage mainly for SentryFileManager and SentrySerialization to cover more edge cases and reduce the probability of introducing bugs by future changes to these critical classes. Furthermore, we want to double-check if some edge cases could lead to unwanted behavior.

Tasks

Beta Give feedback

1. chore: Added UI Test to check invalid envelope is handled correct #4312
   +0
2. impr: Avoid work when storing invalid envelopes #4337
   +0
3. test: Use XCTUnwrap in SerializationTests #4341
   +0
4. test: Add more tests for envelopeWithData #4342
   +0
5. ref: For envelopeWithData serialization #4343
   +0
6. ref: Make AttachmentHeader.contentType to nullable #4344
   +0
7. ref: Serialization use logging macros #4345
   +0
8. test: Add tests for envelopeWithData #4349
   +0
9. test: Switch testCorruptEnvelope to a unit test #4348
   +0
10. fix: Use UInts in envelope deserialization #4441
    +0

[philipphofmann]

The root cause of #4280 was crashing while deserializing a corrupted envelope. We added plenty of new tests to cover more edge cases. This should do it for now.