Description
Reading/writing from the same storage variable more than once should be avoided to save gas.
Recommendation
BRC20Factory::burn() can cache the fee (read twice). Vault::deposit() cache the fee (read thrice).
Vault::acceptAdmin() can cache the pendingAdmin (read 4 times). Vault::withdraw() can cache signers.length (read number of signers times).
Status
Addressed in #68ce26f.