v1.3.5 — Deterministic epoch-boundary gas limit

Deterministic epoch-boundary gas limit

Follow-up from v1.3.3, which temporarily froze the block gas limit at the
parent's value because nt.dynamicScaler.GetCurrentGasLimit() was
producing divergent headers across validators.

Gas limit can now grow and shrink under load — but only at epoch boundaries,
and only via a pure function of parent header fields (block number, parent
gas limit, parent gas used). The computation is identical on every validator
because every validator shares the same parent.

Rule

blockNumber % EpochLength == 0 (epoch boundary):
    if parent.GasUsed * 2 > parent.GasLimit:   raise by parent.GasLimit / 1024
    if parent.GasUsed * 2 < parent.GasLimit:   lower by parent.GasLimit / 1024
    (clamped to [MinBlockGas, MaxBlockGas])
otherwise:
    inherit parent.GasLimit verbatim

This is EIP-1559-style elasticity, restricted to epoch boundaries
(default: every 100 blocks). Under sustained load the gas limit climbs
~0.1%/epoch until it hits the ceiling; under light load it drops similarly
until the floor.

Regression tests

• TestComputeDeterministicGasLimit_NonEpochInheritsParent
• TestComputeDeterministicGasLimit_EpochBoundaryRaises
• TestComputeDeterministicGasLimit_EpochBoundaryLowers
• TestComputeDeterministicGasLimit_Clamps
• TestComputeDeterministicGasLimit_DeterministicAcrossNodes
• TestComputeDeterministicGasLimit_NilParent

Upgrade notes

Drop-in upgrade. No chain data wipe needed. The new formula uses only
parent fields so existing chains continue seamlessly.