test: remove Nimble

[armcknight]

This was added as a team experiment, but recently we decided not to move forward with it.

Lately, it has been causing me pain on every branch switch. Because SPM still has so many problems in Xcode, I would have to manually re-resolve packages to be able to run tests again. No network connection? Well, now you can't resolve the packages, so local testing ¯\(ツ)/¯ This is the only thing we use SPM for in our SDK project, so will be a marked improvement to jettison.

There are several other reasons we decided not to move forward with Nimble, but I'm not going to repeat them here at this time.

Contains a couple other small fixes, like converting some more IUOs to try XCTunwrap, XCTAssertTrue->XCTAssert, XCTAssertEqual(..., nil)->XCTAssertNil etc

#skip-changelog

[codecov]

Codecov Report

Attention: Patch coverage is 99.76581% with 2 lines in your changes missing coverage. Please review.

Project coverage is 91.340%. Comparing base (5be7a7c) to head (a5b349c).

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #4120       +/-   ##
=============================================
+ Coverage   91.339%   91.340%   +0.001%     
=============================================
  Files          610       610               
  Lines        48414     48422        +8     
  Branches     17317     17351       +34     
=============================================
+ Hits         44221     44229        +8     
+ Misses        4101      4100        -1     
- Partials        92        93        +1     

Files	Coverage Δ
...entryTests/Categories/SentryNSDataUtilsTests.swift	100.000% <100.000%> (ø)
...entryTests/Helper/SentryAppStateManagerTests.swift	100.000% <100.000%> (ø)
Tests/SentryTests/Helper/SentryAppStateTests.swift	100.000% <100.000%> (ø)
Tests/SentryTests/Helper/SentryDateUtilTests.swift	100.000% <100.000%> (ø)
...yTests/Helper/SentryDependencyContainerTests.swift	100.000% <100.000%> (ø)
...sts/Helper/SentryEnabledFeaturesBuilderTests.swift	100.000% <100.000%> (ø)
...Tests/Helper/SentryExtraContextProviderTests.swift	100.000% <100.000%> (ø)
...ts/SentryTests/Helper/SentryFileManagerTests.swift	99.119% <100.000%> (ø)
.../SentryTests/Helper/SentrySerializationTests.swift	98.009% <100.000%> (ø)
...ests/SentryTests/Helper/SentryTimeSwiftTests.swift	100.000% <100.000%> (ø)
... and 54 more

... and 5 files with indirect coverage changes

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[brustolin]

Thanks!!

[philipphofmann]

Thanks a lot @armcknight 🥇