Do not emmit confusing warning from FusionOptimizer by default

[ricardoV94]

Description

This warning is confusing and has detracted dev work in case it is likely to not matter at all. Since we are not actively pushing the C-backend anymore seems like a good time as any to stop emitting it by default. Now it's only triggered when optimizer_verbose is True (by default it's not)

We still need to address the fact that the absense of a C-implementation may be leading to less fusion in unrelated backends (only Numba atm, since we don't fuse stuff for JAX, they do it themselves).

Related Issue

• Related to FusionOptimizer truncation logic should be backend specific #140
• Related to Add betainc C implementation #673

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):