fix(gravity): clamp batch timeout projection height

[jamilahmadzai]

Summary

Fixes #945.

This clamps the local ME height used by GetBatchTimeoutHeight when the stored LastObservedBlockHeight.BlockHeight is ahead of the current context height, which can happen after genesis import or migration. Instead of subtracting a larger imported local height from a fresh height-1 context and underflowing uint64, the projection now treats elapsed local time as zero until the chain catches up.

The external observed height is preserved, and the normal timeout window is still added on top of that height.

Validation

• go test ./x/gravity/keeper -run 'TestGravityKeeperTestSuite/TestBatchTimeoutHeightDoesNotUnderflowWhenObservedLocalHeightAhead' -count=1 -v
• go test ./x/gravity/keeper -count=1
• go test ./x/gravity/... -count=1
• go test ./... -count=1
• git diff --check

Payout

Meta Earth bug bounty payout in $MEC via ME Pass wallet:

me1ya82w6cjflk9r2qeyfeu64sm7gxtfr7mu62w9j