[Shellghostt]

Description

package_version() in sentry_sdk/utils.py rebuilt the full installed-package mapping on every call: _get_installed_modules() iterates importlib.metadata.distributions() (parsing every installed distribution's metadata), and package_version additionally re-normalized that whole mapping per call. Integrations call package_version during sentry_sdk.init() to check minimum versions, so in environments with a few hundred installed packages this scan measurably slowed SDK startup.

This change makes package_version look up the single requested distribution with importlib.metadata.version() instead:

• Top-level guarded from importlib import metadata as importlib_metadata (no inline imports, per the repo guidelines); PackageNotFoundError maps to None, matching the previous behaviour for missing packages.
• The existing _get_installed_modules() scan remains as the fallback for environments without importlib.metadata (Python < 3.8), so supported old interpreters keep working.
• Name handling is unchanged: the requested name is PEP 503-normalized first, which is also how importlib.metadata.version() resolves distribution names.

Tests in tests/test_utils.py:

• test_package_version_installed_package asserts an installed package (pytest) resolves to the same parsed version as importlib.metadata.
• test_package_version_does_not_scan_all_installed_packages monkeypatches _get_installed_modules to fail if invoked (the only way to assert the scan no longer happens) and asserts both hit and miss lookups still work.

Validation:

• TESTPATH=tests/test_utils.py uv run tox -e py3.12-common -- -k package_version — 3 passed.
• uv run ruff check / ruff format --check on the changed files — clean.
• uv run --group typing mypy sentry_sdk — no issues in 203 files.

Issues

• resolves: package_version() parses every installed package's metadata, slowing sentry_sdk.init() #8190

Reminders

• Tests added and linted with uv run ruff as requested.
• PR title uses conventional-commit style.