cons/grep: remove global state

[XVilka]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository
• I made sure to follow the project's coding style
• I've documented or updated the documentation of every function and struct this PR changes. If not so I've explained why.
• I've added tests that prove my fix is effective or that my feature works (if possible)
• I've updated the rizin book with the relevant information (if needed)

Detailed description

Remove globals and statics from the grep implementation.

Test plan

CI is green

Closing issues

Partially addresses #4055
Partially addresses #276

[wargio]

nice <3