fix: explicit SKIPPED status for Tor/I2P/DNS sites when no proxy is configured

[mvanhorn]

Summary

In the dispatch path (maigret/checking.py around line 852, right after checker = make_protocol_checker(options, site.protocol)), detect when the resolved checker is the no-op mock via isinstance(checker, CheckerMock) and short-circuit before the request is attempted. Instead of dispatching to the mock, build a MaigretCheckResult with MaigretCheckStatus.ILLEGAL plus an explanatory CheckError("Skipped", "no <protocol> gateway configured"), mirroring the existing disabled-site branch (checking.py ~860) that already renders cleanly in CLI and JSON. Reusing ILLEGAL keeps the change to a single file and avoids touching the report/rendering layer (no new enum value to plumb through maigret/report.py), while still satisfying the acceptance criteria: no "Connection lost" entries for .onion/.i2p/domain sites and a one-line skip explanation in the report.

Why this matters

When the user does not pass --tor-proxy / --i2p-proxy / --with-domains, the corresponding protocol checker is resolved to a CheckerMock (maigret/checking.py:599) whose check() returns ('', 0, None). A status_code of 0 is later interpreted as CheckError("Connection lost"), so every .onion / .i2p / domain entry reports a fake "Connection lost" error instead of being honestly skipped. This pollutes --print-errors, masks real connection-lost errors on clearweb sites, and is misleading because the site was never actually contacted. The issue was filed by the maintainer (soxoj) with detailed code refs and acceptance criteria; a contributor noted the exact symptom string has drifted, but the underlying CheckerMock mechanism is unchanged on current main (verified at checking.py:599-610 and the proxy-absent fallbacks at checking.py:1121-1138).

See #2664.

Testing

• Happy path: clearweb site with a real checker still reaches the normal request path and reports CLAIMED/AVAILABLE unchanged. - Edge case: .onion site dispatched with no --tor-proxy yields a skipped result with an explanatory message, and --print-errors shows no "Connection lost" entry for it. - Edge case: .i2p and domain (DNS) sites behave identically when their proxy/option is absent. - Error path: a genuine clearweb connection failure still surfaces as a real CheckError("Connection lost") and is not swallowed by the new skip branch.

Fixes #2664