Add "Classic" Style Accel

[catprocessor]

The only thing this program is missing is classic style acceleration. It'd be great to have an option for it, considering an easy classic formula is just raising the linear acceleration formula to an exponent > 2.

(By the way, I would be willing to pay, sponsor, or donate $100 USD minimum if it were added...)

[SimoneMariaRomeo]

I opened a focused PR for this: #115

What it adds:

• CLASSIC_EXPONENT for the existing linear/classic curve
• default 2.0, preserving current behavior
• CLI/TUI parameter exposure as classic-exponent
• NixOS module exposure as classicExponent
• a small driver-level assertion that exponent 3 produces a stronger high-speed curve than exponent 2

Validation: git diff --check passed. I could not run Cargo/driver tests in this Windows environment because Cargo/Rust/C toolchains are not installed and Docker is not running, so this is source-level proof pending Linux CI or maintainer testing.

If this matches what you meant by classic-style acceleration and you want to support the work, the dedicated USD 100 payment link is:
https://buy.stripe.com/00w6oA5zVgGZ5ntaWMbZe0W

[catprocessor]

Hi: I made this post without realizing people might pull request and fork it to add the change themselves. Whichever pull request the main branch goes with I will try to donate to the author to, in addition to gnarus and the project itself