feat: Implement custom logging initialization for SP1 package

[huitseeker]

Configures logging for go through an environment variable.

Example usage:

SP1_GO_LOG=false cargo test

./cargo test
SP1_GO_LOG=debug ./cargo test

This solution works because:

• The init() function in logging.go will run before any other code in the package
• Since gnark uses zerolog, setting the global log level will affect all logging throughout the application, including in dependencies
• The change is minimal and contained to just one file (as long as the main.go module early-loads the sp1 package)
• It doesn't require any changes to the Rust code or to gnark's source code
• It's configurable through an environment variable

[wwared]

This is a great and elegant solution! I didn't even know about Go's init functions, very nice!

There's two situations where the Go code is still printing even with logging disabled (after a couple quick tests on my end):

• When making the artifacts, it prints information related to fetching and verifying the aztec ignition srs data. This is a non-issue we can live with
• When verifying a proof in the FFI lurk-hs context, it seems to still print the "ignoring uninitialized slice: Vars []frontend.Variable" message 3 times. This is unfortunately a regular fmt.Printf call inside of gnark, either here or here

The latter seems a bit trickier to solve neatly. It might be easier for us to do a minimal patch to the sphinx-recursion-gnark-ffi go code to properly initialize the slices gnark is referring to in the messages rather than trying to patch out the printf call (though I don't know what exactly we should initialize them to). We can also make a minimal gnark upstream PR changing those two prints to warning log messages (which might be the best overall solution for everyone)

I've opened Consensys/gnark#1305 upstream to solve the latter issue