fix(discovery): use layout-descriptor offsets for all V1-family engine parsing

[0x-SquidSol]

Summary

• parseEngineLight's layout-driven branch was gated on V_ADL-specific constants (engineOff===624 && accountSize===312)
• V12.1 SBF (engineOff=616, accountSize=280), V12.1 HOST, V_SETDEXPOOL, V1M2, V1, V1D, V1M all fell through to the V1 hardcoded fallback with wrong offsets (24-byte shift from markPrice onward, and completely wrong for non-V1 layouts)
• This is the same fix as merged PR fix(discovery): use layout-descriptor offsets for all V1-family engines #151 but with critical additions: >= 0 guards on 10 engine fields that V12.1 SBF sets to -1 (fundingIndex, lastFundingSlot, totalOi, insurance isolation, LP aggregates, lifetime force closes)
• Without these guards, widening the branch to layout !== null would crash on V12.1 SBF slabs (reading at base + (-1))
• The V1 hardcoded fallback (which also had a systematic 24-byte offset error) is removed as dead code
• Forward-compatible: any new layout version only needs a buildLayout*() helper — no new branch in parseEngineLight

Test plan

• Discovery tests pass (60/60)
• No new test failures (16 pre-existing failures from HOST bitmapOff + ADL mock issues are separate)
• Verify V12.1 SBF slabs produce correct engine state via discoverMarkets
• Verify V_ADL, V1, V1D slabs still parse correctly (regression)

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Reviewing files that changed from the base of the PR and between 2f80d79 and d322864.

📒 Files selected for processing (1)

• src/solana/discovery.ts

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