feat: carry simulation v2 - fix gains precision + add funding + GMX carry

[Flotapponnier]

What

• Fix bToASim symmetric: HL→Gains projection (venueB=HL, venueA=Gains) was missing gainsFunding — now matches the aToBSim path
• Fix Gains precision bug: GAINS_BORROW_PRECISION was 1e10 × per-block (1000x too high); corrected to 1e18 per-second via collaterals[3].borrowingFees.v2.pairParams
• Add Gains funding projection: estimateGainsFundingFees() reads collaterals[3].fundingFees.pairData[i].lastFundingRatePerSecondP / 1e18; applied to both aToBSim and bToASim
• Add GMX carry projection: when HL trades are projected onto GMX (or vice versa), uses the wallet's own GMX history to derive implied borrow + funding rates and applies them to the HL notional

Projection coverage after this PR

Direction	Taker	Borrow	Funding
HL → Gains	✓ per-coin	✓ v6 per-sec	✓ v6 per-sec
Gains → HL	✓ per-coin	-	✓ 8h history
HL → GMX	✓	✓ implied	✓ implied
GMX → HL	✓	-	-