fix(rule): raise SigmaError for non-string related fields and non-map detection

[nkbeast]

Fixes malformed rules crashing with raw exceptions instead of proper validation errors.

What's broken

SigmaRule.from_yaml/from_dict is supposed to validate malformed rules and produce SigmaErrors (collected via collect_errors=True or raised otherwise). Three malformed-rule shapes bypass that machinery and crash callers (e.g. sigma-cli batch checks) with raw exceptions:

1. related: [{id: 123, type: derived}] — non-string id inside an otherwise valid map.
   UUID(123) raises AttributeError (only ValueError is caught), so the rule crashes instead of raising SigmaRelatedError.

2. related: [{id: ..., type: 123}] — non-string type hits .upper() under a bare except, producing a SigmaRelatedError only by accident of the catch-all.

3. detection: hello (or detection: [a, b], detection: 123) — a non-map detection section.
   detections["condition"] raises TypeError, which is not caught in SigmaRule.from_dict, so parsing crashes even with collect_errors=True.

Fix

• SigmaRelatedItem.from_dict validates that id and type are strings before use, raising SigmaRelatedError (mirrors the isinstance style of the earlier type-validation fix for related: [foo]).
• SigmaRule.from_dict gains an except TypeError branch for the detection block, mirroring the existing guard in SigmaFilter.from_dict ("Sigma filter must be a dictionary").

All three shapes now yield a collected/raised SigmaDetectionError / SigmaRelatedError like every other rule error.

Tests

Added 3 regression tests in tests/test_rule.py:

• test_invalid_related_id_type — id: 123 raises SigmaRelatedError
• test_invalid_related_type_type — type: 123 raises SigmaRelatedError
• test_sigmarule_detection_not_map / test_sigmarule_detection_not_map_collect_errors — non-map detection raises / collects SigmaDetectionError

Verification

• pytest tests/test_rule.py — 148 passed
• Full suite — 1525 passed, 1 skipped (2 pre-existing plugin-install failures need network/pip)
• mypy — clean (66 files)
• black --check — clean