Make proof function prefix configurable

[palinatolmach]

Originally posted by @tothtamas28 in #249 (comment)

The logic for deciding what sort of KCFG to construct based on the function name (e.g., starting with test, prove, etc.) should be pulled up from the _method_to_cfg function, and is_test and failing should become parameters.

Halmos allows specifying the function name using the following argument, and we can do the same thing, introducing, e.g., --function and --fail-function as the first step:

    parser.add_argument(
        "--function",
        metavar="FUNCTION_NAME_PREFIX",
        default="check_",
        help="run tests matching the given prefix. Shortcut for `--match-test '^{PREFIX}'`. (default: '%(default)s')",
    )

On the other hand, as also noted by @tothtamas28, proof name prefix is not something that's likely to change between kontrol prove calls so we may not want to expose it on the CLI.

As a better alternative, proof_prefixes is the sort of thing that should be configurable through a configuration file. If it doesn't break Foundry we can consider adding a section to foundry.toml (e.g., [kontrol] or [symbolic]), which won't break Foundry but will throw a warning:

warning: Found unknown config section in foundry.toml: [kontrol]
This notation for profiles has been deprecated and may result in the profile not being registered in future versions.
Please use [profile.kontrol] instead or run `forge config --fix`.

Otherwise, maybe its time to introduce kontrol.toml. This would enable cleaning up the CLI a bit as well. We have this issue on our roadmap for February, but it can also be picked up earlier if we have the bandwidth.