fix: use coverage run instead of pytest --cov for accurate import-time coverage

The pytest11 entry point (`zarr = "zarr.testing"`) imports 76 zarr modules
during plugin loading, before pytest-cov starts measuring. This caused all
module-level code (class definitions, imports, decorators) to appear uncovered,
dropping reported coverage well below actual test coverage.

`coverage run -m pytest` starts tracing before any imports, resolving the issue.

Author: maxrjones

pyproject.toml

@@ -142,6 +142,7 @@ exclude_also = [
 [tool.coverage.run]
 omit = [
     "bench/compress_normal.py",
+    "src/zarr/_version.py",  # auto-generated by setuptools-scm
     "src/zarr/testing/conftest.py",  # only for downstream projects
 ]
 
@@ -155,10 +156,6 @@ hooks.vcs.version-file = "src/zarr/_version.py"
 dependency-groups = ["test"]
 
 [tool.hatch.envs.test.env-vars]
-# Required to test with a pytest plugin; see https://pytest-cov.readthedocs.io/en/latest/plugins.html
-COV_CORE_SOURCE = "src"
-COV_CORE_CONFIG = "pyproject.toml"
-COV_CORE_DATAFILE = ".coverage.eager"
 
 [[tool.hatch.envs.test.matrix]]
 python = ["3.12", "3.13", "3.14"]
@@ -175,13 +172,23 @@ matrix.deps.dependency-groups = [
 ]
 
 [tool.hatch.envs.test.scripts]
-run-coverage = "pytest --cov-config=pyproject.toml --cov=src --cov-report xml --junitxml=junit.xml -o junit_family=legacy"
-run-coverage-html = "pytest --cov-config=pyproject.toml --cov=src --cov-report html"
-run = "run-coverage --no-cov --ignore tests/benchmarks"
+run-coverage = [
+    "coverage run --source=src -m pytest --junitxml=junit.xml -o junit_family=legacy {args:}",
+    "coverage xml",
+]
+run-coverage-html = [
+    "coverage run --source=src -m pytest {args:}",
+    "coverage html",
+]
+run = "pytest --ignore tests/benchmarks"
 run-verbose = "run-coverage --verbose"
 run-mypy = "mypy src"
-run-hypothesis = "run-coverage -nauto --run-slow-hypothesis tests/test_properties.py tests/test_store/test_stateful*"
+run-hypothesis = [
+    "coverage run --source=src -m pytest -nauto --run-slow-hypothesis tests/test_properties.py tests/test_store/test_stateful* {args:}",
+    "coverage xml",
+]
 run-benchmark = "pytest --benchmark-enable tests/benchmarks"
+serve-coverage-html = "python -m http.server -d htmlcov 8000"
 list-env = "pip list"
 
 [tool.hatch.envs.gputest]
@@ -195,8 +202,11 @@ features = ["gpu"]
 python = ["3.12", "3.13"]
 
 [tool.hatch.envs.gputest.scripts]
-run-coverage = "pytest -m gpu --cov-config=pyproject.toml --cov=src --cov-report xml --junitxml=junit.xml -o junit_family=legacy --ignore tests/benchmarks"
-run = "run-coverage --no-cov"
+run-coverage = [
+    "coverage run --source=src -m pytest -m gpu --junitxml=junit.xml -o junit_family=legacy --ignore tests/benchmarks {args:}",
+    "coverage xml",
+]
+run = "pytest -m gpu --ignore tests/benchmarks"
 
 [tool.hatch.envs.upstream]
 template = 'test'