MNT: Run coverage directly instead of using pytest-cov

pytest-cov ends up invoking coverage *after* the warning filter, which
means coverage starts after many submodules are imported.

.coveragerc

@@ -0,0 +1,10 @@
+[paths]
+source =
+    src/
+    /*/site-packages
+
+[run]
+source = tests
+source_pkgs = metpy
+omit =
+    src/metpy/io/_nexrad_msgs/parse_spec.py

.github/workflows/tests-conda.yml

@@ -85,9 +85,13 @@ jobs:
         python -m pip install --no-deps .
 
     - name: Run tests
+      # By running coverage in "parallel" mode and "combining", we can clean up the path names
       run: |
         export TEST_DATA_DIR=$GITHUB_WORKSPACE/staticdata
-        python -m pytest --mpl -W error::metpy.deprecation.MetpyDeprecationWarning --cov=metpy --cov=tests --cov-report=xml
+        python -m coverage run -p -m pytest --mpl -W error::metpy.deprecation.MetpyDeprecationWarning tests/
+        python -m coverage combine
+        python -m coverage report
+        python -m coverage xml
 
     - name: Run doctests
       # Windows produces some slightly different types that causes doctests to fail

.github/workflows/tests-pypi.yml

@@ -107,7 +107,10 @@ jobs:
       run: |
         export TEST_DATA_DIR=$GITHUB_WORKSPACE/staticdata
         export NUMPY_EXPERIMENTAL_ARRAY_FUNCTION=1
-        python -m pytest --mpl -W error::metpy.deprecation.MetpyDeprecationWarning --cov=metpy --cov=tests --cov-report=xml
+        python -m coverage run -p -m pytest --mpl -W error::metpy.deprecation.MetpyDeprecationWarning tests/
+        python -m coverage combine
+        python -m coverage report
+        python -m coverage xml
 
     - name: Run doctests
       if: ${{ matrix.dep-versions == 'Current.txt' && matrix.no-extras != 'No Extras' }}

.travis.yml

@@ -81,7 +81,10 @@ script:
         false;
       fi;
     else
-      python -m pytest --mpl -W error::metpy.deprecation.MetpyDeprecationWarning --cov=metpy --cov=tests;
+      python -m coverage run -p -m pytest --mpl -W error::metpy.deprecation.MetpyDeprecationWarning tests/;
+      python -m coverage combine;
+      python -m coverage report;
+      python -m coverage xml;
     fi
 
 after_script:

ci/test_requirements.txt

@@ -1,4 +1,4 @@
 pytest==6.1.0
-pytest-cov==2.10.1
 pytest-mpl==0.11
 netCDF4==1.5.4
+coverage==5.3

setup.cfg

@@ -96,9 +96,6 @@ norecursedirs = build docs .idea
 doctest_optionflags = NORMALIZE_WHITESPACE
 mpl-results-path = test_output
 
-[coverage:run]
-omit = src/metpy/io/_nexrad_msgs/parse_spec.py,src/metpy/io/metar_parser.py
-
 [doc8]
 ignore-path = docs/build,docs/api/generated,docs/_templates,docs/tutorials,docs/examples
 file-encoding = utf8