contrib: deterministic-fuzz-coverage fixups

* Name the fuzz_corpora dir after its real name.
* Add missing cargo lock file.
* Use git instead of diff command to increase compatibility
* Use --help instead of --version to increase compatibility
* Use assert consistently for unexpected errors.
* Remove redundant Stdio::from.
* Fix typos.

contrib/devtools/README.md

@@ -22,7 +22,7 @@ repository must have been cloned. Finally, a fuzz target has to be picked
 before running the tool:
 
 ```
-RUST_BACKTRACE=1 cargo run --manifest-path ./contrib/devtools/deterministic-fuzz-coverage/Cargo.toml -- $PWD/build_dir $PWD/qa-assets/corpora-dir fuzz_target_name
+RUST_BACKTRACE=1 cargo run --manifest-path ./contrib/devtools/deterministic-fuzz-coverage/Cargo.toml -- $PWD/build_dir $PWD/qa-assets/fuzz_corpora fuzz_target_name
 ```
 
 clang-format-diff.py