fix(capacitors): validate maxPacketLength_ input instead of stale state

[HusseinAdeiza]

Summary

HashChainCapacitor validates the stale maxPacketLength state variable instead of its own input maxPacketLength_ in both the constructor and updateMaxPacketLength, so the MAX_LEN (10) guard never rejects anything: the constructor checks the default 0, and the update path re-checks the already-set value. Oversized packet lengths install silently. Swapping the two checks to the input fixes it.

Fixes #436

Test plan

Three regression tests added to test/capacitors/HashChainCapacitor.t.sol: oversized constructor input and oversized update input must revert with InvalidPacketLength (both fail on current master), and the boundary value 10 stays accepted.

forge test --match-path test/capacitors/*
# 28 passed, 0 failed

Both changed files pass prettier@2.8.8 --check with prettier-plugin-solidity at the repo-pinned version.