refactor(osv-linter): tidy up human output

[andrewpollock]

• Add a --verbose flag to tone down the output
• Clean up how the findings are presented
• Discovered the Alpine ecosystem was being overlooked in error

$ go run ./cmd/osv record lint test_data/
test_data/nointroduced-CVE-2023-41045.json:
         * [R0001]: missing 'introduced' object in event
test_data/nondistinct-CVE-2018-5407.json:
         * [R0002]: overlapping event: "e818b74be2170fbe957a07b0da4401c2b694b3b8"
test_data/nopackage-GHSA-9v2f-6vcg-3hgv.json:
         * [P0001]: package "Gradi0" not found in "PyPI"
         * [P0002]: Failed to find some versions of Gradi0: &errors.errorString{s:"unable to validate package: fail: \"https://pypi.org/pypi/gradi0/json\": bad response: 404"}
2024/09/04 06:42:12 found errors
exit status 1