[testing] Switch to logging with zap

[marun]

Why this should be merged

Previously testing used an incoherent mix of TestContext.Outf, fmt.Print and fmt.Fprint. This PR switches everything to use the zap logger for consistency with the rest of avalanchego.

How this works

• switches fixture like tmpnet and the e2e helpers to zap
• updates all tests to use zap

How this was tested

CI

TODO

• Figure out why the logger returned by NewSimpleLogger is outputting weird level e.g. Level(-6) instead of INFO

Need to be documented in RELEASES.md?

N/A

[StephenButtolph]

We have modified how levels are encoded. We should be providing a custom leveler like in the rest of avalanchego:

func levelEncoder(l zapcore.Level, enc zapcore.PrimitiveArrayEncoder) {
	enc.AppendString(Level(l).String())
}

func jsonLevelEncoder(l zapcore.Level, enc zapcore.PrimitiveArrayEncoder) {
	enc.AppendString(Level(l).LowerString())
}

See utils/logging/format.go#newTermEncoderConfig

[marun]

Any objection to exporting these functions so they can be reused?

[StephenButtolph]

Nope - makes sense to me.

[marun]

Done