feat(api): Ergonomic improvements and derive macro for FuzzerState

[venkkatesh-sekar]

This PR introduces significant ergonomic improvements to the canfuzz API, making it easier and less verbose to set up new fuzzers.

Key Changes

1. Builders for Configuration:
   • Introduced CanisterBuilder and FuzzerBuilder to simplify the creation of CanisterInfo and FuzzerState.
   • CanisterBuilder supports a fluent interface for setting properties like Wasm path (file or env var), canister type (coverage/support), and initialization arguments.
2. Automated Environment Setup:
   • Added FuzzerState::setup_canisters() method. This helper automates the initialization of PocketIc, creation of canisters, and installation of Wasm modules, replacing ~10-15 lines of boilerplate in the init() method of every fuzzer.
3. Standard Traits & Derive Macro:
   • Replaced the custom FuzzerStateProvider trait with standard AsRef<FuzzerState> and AsMut<FuzzerState> bounds on FuzzerOrchestrator.
   • Introduced a new canfuzz_derive crate (exposed via the derive feature in canfuzz) providing a #[derive(FuzzerState)] macro. This automatically implements the required traits for fuzzer structs wrapping FuzzerState.
4. Canister Initialization Arguments:
   • Added support for passing initialization arguments to canisters via CanisterBuilder::with_init_args(Option<Vec<u8>>).

Before:

struct MyFuzzer(FuzzerState);
impl FuzzerStateProvider for MyFuzzer {
    fn get_fuzzer_state(&self) -> &FuzzerState { &self.0 }
}
// ... inside FuzzerOrchestrator implementation ...
fn init(&mut self) {
    let test = PocketIcBuilder::new()...build();
    self.0.init_state(test);
    let test = self.get_state_machine();
    // Manual loop to create and install canisters...
}

After:

#[derive(FuzzerState)]
struct MyFuzzer(FuzzerState);
// ... inside FuzzerOrchestrator implementation ...
fn init(&mut self) {
    self.as_mut().setup_canisters();
}
fn main() {
    let target = CanisterBuilder::new("target")
        .with_wasm_path("target.wasm")
        .as_coverage()
        .build();
    
    let state = FuzzerBuilder::new()
        .with_canister(target)
        .build();
        
    MyFuzzer(state).run();
}