Fix assert.ErrorContains for nil error

[byo]

Note

Make ErrorContains fail with a clear message when given a nil error and add a test covering this case.

• Assertions (picotestify/assert):
  • Update ErrorContains to explicitly handle nil errors and produce a specific failure message.
  • Add test case "ErrorContains - nil" to verify the new behavior.

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[coveralls]

Pull Request Test Coverage Report for Build 19395531633

Details

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 19003035256:	0.0%
Covered Lines:	494
Relevant Lines:	494

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💛 - Coveralls