Switched to using cargo-llvm-cov for coverage

This is simpler to use and also cleaner.

Makefile

@@ -1,13 +1,9 @@
-build-dev:
-	cargo build --tests
+setup-coverage-tools:
+	cargo +stable install cargo-llvm-cov --locked
 
-setup-grcov:
-	cargo install grcov
+coverage: setup-coverage-tools
+	cargo llvm-cov --open
 
-coverage: build-dev setup-grcov
-	RUSTFLAGS="-C instrument-coverage" cargo test
-	grcov . -s . --binary-path ./target/debug/ -t html --branch --ignore-not-existing -o ./target/debug/coverage/
-	rm *.profraw
 
 setup-rust-checks:
 	rustup component add rustfmt