[FEATURE] Add mypy coverage outside fo opensearchpy/*

[dblock]

Is your feature request related to a problem?'

Coming from #563 where we merged type stubs. Add type coverage for tests, benchmarks, etc.

What solution would you like?

Edit noxfile, fix type errors.

+++ b/noxfile.py
@@ -82,7 +82,7 @@ def lint(session) -> None:
 
     # Run mypy on the package and then the type examples separately for
     # the two different mypy use-cases, ourselves and our users.
-    session.run("mypy", "--strict", "opensearchpy/")
+    session.run("mypy", "--strict", *SOURCE_FILES)
     session.run("mypy", "--strict", "test_opensearchpy/test_types/sync_types.py")
     session.run("mypy", "--strict", "test_opensearchpy/test_types/async_types.py")

[dblock]

Current state of https://github.com/dblock/opensearch-py/tree/rest-of-mypy

$ nox -rs format 

Found 237 errors in 61 files (checked 221 source files)
nox > Command mypy --strict setup.py noxfile.py opensearchpy/ test_opensearchpy/ utils/ samples/ benchmarks/ docs/ failed with exit code 1