test: densify ctest suite — line coverage 86.4% → 93.1% (tests-only)

[luisleo526]

Summary

Densifies the ctest unit suite so passing it more strongly underwrites "~95% of pinescript reproduced." Tests + coverage-tooling only — zero src//include/ changes.

• ctest: 53 → 68 unit tests, 100% pass under the canonical Release (-DNDEBUG) gate.
• Line coverage: 86.38% → 93.06% (+6.68 pts, 499 fewer missed lines).
• TV corpus parity unchanged (245 excellent + 1 anomaly, no drift).

15 new tests target the lowest-covered translation units, pinning real Pine-correct behavior via closed-form OHLC oracles and na/warmup edge cases.

Per-TU line coverage

TU	before	after
c_abi	16%	100%
engine_report	73%	100%
ta_moving_averages	93%	100%
ta_extremes_volume	95%	99%
ta_oscillators	95%	99%
ta_volatility_trend	94%	97%
engine_strategy_commands	92%	96%
engine_fills	94%	96%
engine_lower_tf	88%	95%
engine_path_resolve	78%	94%
engine_run	79%	93%
engine_security	86%	93%
matrix	88%	98%
timeframe	89%	94%
session_time	68%	90%

NDEBUG-proof tests

The prescribed gate builds Release (-DNDEBUG), which no-ops bare assert() and makes assert-only tests pass vacuously. All new tests use a self-rolled CHECK + failure-counter return instead; non-vacuity was confirmed by corrupt-and-rebuild. (Note: the pre-existing test_security_tf_validation.cpp has this latent assert()/NDEBUG defect — flagged, out of scope here.)

Coverage tooling (scripts/)

• coverage.sh: fix uncovered.txt sort key (was sorting by region cov col 4, now line cov col 10); capture llvm-cov's "N functions have mismatched data" warning — benign (header inline/template code instantiated across all test binaries with differing mapping hashes; the merge drops unmatched variants) — and replace it with a plain-language NOTE.
• cov_union.py: on-demand per-binary union verifier for exact header line coverage (recovers the multi-binary undercount, e.g. generic_matrix.hpp ~77% reported → ~86% true). .cpp headline metric unchanged.

Verification

• ctest 68/68 pass (Release).
• scripts/run_corpus.sh parity unchanged.
• No src/ or include/ diffs.

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