Drift check: harden classifier and add coverage/infra-failure buckets

[dkijania]

Stacked on #26 — review/merge that one first; rebase this on master afterward.

Summary

Two-layer schema-drift checker:

1. Introspection diff (Layer 1) — now also detects argument-type changes (e.g. UInt64 → TokenId) and inputField-type changes that the previous version silently passed. The exact bug fixed in Fix GET_ACCOUNT_WITH_TOKEN type + refresh schema snapshot #26 is the kind of drift this layer is supposed to catch.
2. Live query check (Layer 2) — parses src/mina_sdk/daemon/queries.py, sends each operation with sentinel variables, classifies GraphQL errors. Drift patterns are matched against the message before the path-based runtime fallback (Mina attaches path to many validation errors, so the previous path-first short-circuit dropped real drift to runtime). Bare "expected type" was removed from drift patterns (false-positives on value coercion); a regex for the "expected on field X, found Y" shape routes those to runtime.

Hardening (from internal review)

• httpx.Client with 30 s timeout
• HTTP status check (non-2xx → error; was silently treated as "OK" when body parsed but had no errors key)
• normalize_schema raises on error envelopes — no silent fake-empty schema that flagged every type as REMOVED
• _name_of safe against null / non-dict entries in introspection arrays
• kind nil-guard avoids spurious <None> -> X diffs
• _OP_RE filters to bodies that actually start with query|mutation|subscription, so unrelated triple-quoted constants don't get probed
• _VARS_RE anchored to body start so inner field-arg parens like bestChain(maxLength: 1) can't bind
• Connection / HTTP errors counted as infra failures, not drift; always exit 1
• SKIPped ops (stale sentinel table) fail in --strict

Test plan

• Clean run against compatible-latest-lightnet in --strict: exit 0, 11 ok, 0 drift, 2 runtime, 0 skipped, 0 infra-failures.
• Same negative cases as the Go PR (arg-type drift, inputField-type drift, unknown-field, unknown input type, unreachable port) all behave as expected.

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