chore: Refactor pprof dependency

- Shifted `pprof` from `dev-dependencies` to `dependencies` for non-wasm32 targets to optimize benchmarking builds.
- Introduced "flamegraph" feature to include `pprof` during benchmarking.
- Closes lurk-lang#309

Cargo.toml

@@ -57,9 +57,9 @@ getrandom = { version = "0.2.0", default-features = false, features = ["js"] }
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 proptest = "1.2.0"
+pprof = { version = "0.13", optional = true } # in benches under feature "flamegraph"
 
 [target.'cfg(not(target_arch = "wasm32"))'.dev-dependencies]
-pprof = { version = "0.13" }
 criterion = { version = "0.5", features = ["html_reports"] }
 
 [dev-dependencies]