pack: return error when no devices match

[giri256]

Fixes #1130.

pyocd pack find and pyocd pack install currently return success when no device matches the requested pattern. This makes failed lookups indistinguishable from successful commands in scripts.

The modern subcommands and their deprecated --find / --install equivalents now return status 1 when the match set is empty. The behavior of pack update is unchanged because a metadata refresh can partially succeed, as discussed in the issue.

Tests:

• pytest test/unit/test_pack_cmd.py -q — 4 passed
• pytest test/unit -q — 1104 passed, 41 skipped
• flake8 pyocd test --count --select=E9,F63,F7,F82 --show-source --statistics — 0 errors
• python test/import_all.py — 372 modules imported
• python -m build
• twine check dist/* — wheel and source archive passed
• git diff --check