chore[tool]: update coverage exclusion rules

improve coverage by updating coverage exclusion rules to exclude
statements/branches we don't expect to hit at runtime (like panics or
type checking)

setup.cfg

@@ -45,3 +45,11 @@ omit = vyper/version.py
 # allow `coverage combine` to combine reports from heterogeneous OSes.
 # (mainly important for consolidating coverage reports in the CI).
 relative_files = True
+
+[coverage:report]
+# see https://coverage.readthedocs.io/en/latest/excluding.html#advanced-exclusion
+exclude_also =
+    if TYPE_CHECKING:
+    def __repr__
+    raise CompilerPanic
+    raise TypeCheckFailure