fuzzgen: Statistics framework (#4868)

* cranelift: Add non user trap codes function

* cranelift: Add Fuzzgen stats

* cranelift: Use `once_cell` and cleanup some stuff

* fuzzgen: Remove total_inputs metric

* fuzzgen: Filter empty trap codes

fuzz/Cargo.toml

@@ -9,6 +9,7 @@ cargo-fuzz = true
 
 [dependencies]
 anyhow = { workspace = true }
+once_cell = { workspace = true }
 cranelift-codegen = { workspace = true, features = ["incremental-cache"] }
 cranelift-reader = { workspace = true }
 cranelift-wasm = { workspace = true }