ci: Use cargo-llvm-cov to generate coverage data (#438)

* ci: Use cargo-llvm-cov to generate coverage data

* ci: Remove usage of lld in coverage.yml

* ci: Move codecov.yml to project root

codecov.yml

@@ -0,0 +1,10 @@
+# codecov config
+coverage:
+  status:
+    patch: off # disable patch status
+    project:
+      default:
+        enable: yes
+        threshold: 1%
+ignore:
+  - "**/error*.rs" # ignore all error.rs files