test: over-run polish (compound test + naming consistency)

[zuchka]

Summary

Two small follow-ups from PR #15's final code review:

1. Compound over run AND value engine test — the spec example avg(value) over run > 70 AND value > 95 was covered at the parse level but not at the engine evaluation level. New test TestProcess_OverRunCompoundAND in end_of_run_test.go drives the full chain with a 4-event sequence that exercises both the false-AND-false and true-AND-true cases and verifies the right arm doesn't fire alone when the windowed left arm is below threshold.

2. Test rename — TestRingBuffer_RunBounded_RespectsMaxSize → TestRingBuffer_OverRun_RespectsMaxSize for naming consistency with the spec's testing nomenclature (OverRun is the user-facing concept; RunBounded is the implementation detail). All other related tests use OverRun in their names.

Test plan

• go test ./internal/evaluator/... passes
• go test ./... passes (no regressions)
• New test TestProcess_OverRunCompoundAND covers four event scenarios:
  • Event 1: both arms false → no fire
  • Event 2: both arms false → no fire
  • Event 3: right arm true, left arm false (avg below threshold) → no fire
  • Event 4: both arms true → fires with correct Avg=82.5, Count=4

Note on the third follow-up

The third item from the final review was "version bump to v0.12.0 at release time." That's a tag operation, not a code change — no separate PR commit is needed since DING's version is injected via goreleaser ldflags from the git tag (-X main.version={{.Version}} in .goreleaser.yaml). Once this PR merges, the next step is tagging main as v0.12.0 to trigger the release pipeline.

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