tests: raise sdk-python coverage from 73% to 100%

[TeoSlayer]

Summary

Adds four new test files that bring the four production modules in pilotprotocol/ from 73% → 100% line coverage. No production code was modified.

File	Stmts	Before	After
pilotprotocol/__init__.py	7	71%	100%
pilotprotocol/_runtime.py	216	83%	100%
pilotprotocol/cli.py	15	0%	100%
pilotprotocol/client.py	413	71%	100%
TOTAL	651	73%	100%

Test count: 124 → 204 passing (90 skipped fuzz tests unchanged).

New test files

• tests/test_cli.py (8 tests) — every console-script entry point (run_pilotctl, run_daemon, run_gateway, run_updater) with subprocess.call stubbed so no real binaries run. Verifies argv passthrough, non-zero exit propagation, and that the binary list matches pyproject.toml console_scripts.
• tests/test_services.py (31 tests) — the high-level Driver helpers send_message (port 1001 data-exchange framing), send_file (TypeFile payload layout), publish_event (port 1002 subscribe-then-publish), and subscribe_event (frame parsing + callback mode + every short-read termination + clean EOF + unhandled-error propagation). Uses a FakeConn that records writes and serves canned reads — never touches libpilot or a daemon.
• tests/test_runtime_edges.py (32 tests) — the seeder edge cases the main test file skipped: ETXTBSY skip + reraise of other OSError, atomic-install cleanup on os.replace failure, _ensure_default_config race with another writer, _daemon_running config + socket-close failure paths, _runtime_root PILOT_HOME both branches, runtime_binary / runtime_library wheel fallbacks, _semver_tuple parser edges, ensure_runtime_seeded cache + force=True bypass.
• tests/test_client_edges.py (9 tests) — _find_library ~/.pilot/bin branch, _void_ptr_to_bytes + _free helpers, Conn.read size validation (<= 0 returns empty without an FFI call, > 16MB capped to 16MB), and the __version__ PackageNotFoundError fallback to "unknown".

Approach

All libpilot calls are mocked at the ctypes.CDLL boundary via the same FakeLib pattern the existing test_client.py uses. Service helpers are tested by replacing Driver.dial with a fake that returns a FakeConn, so the wire-format assertions can run without a socket or shared library. The runtime seeder tests redirect PILOT_HOME and _pkg_bin_dir into a tmpdir so no ~/.pilot/ mutation happens on the host.

Test plan

• pytest --cov=pilotprotocol --cov-report=term reports 100% on all four modules
• All 204 tests pass, 0 regressions (90 pre-existing skips unchanged)
• No production code changed (git diff main -- pilotprotocol/ is empty)
• CI workflow at .github/workflows/ci.yml already runs pytest --cov=pilotprotocol so this PR automatically uploads the new coverage to Codecov

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