Running `yarn` causes a diff in the `yarn.lock` file.

fix(ctb): correct usage of legacy in ProxyAdmin

chore(ctb): update semver to 1.0.0

specs: system config unsafe block signer

fix(ctb): minor edit to XDM comment

fix(ctb): comment in SequencerFeeVault

feat(ctb): Forge invariant tests

fix(ctb): remove unnecessary ERC20 factory code

Corrects the usage of the legacy custom tag in the ProxyAdmin contract.
Legacy tags are meant for legacy functions that are included in a
contract in order to satisfy a previous ABI. The ProxyAdmin was using
legacy tags for things that have to do with legacy behavior.

Updates semver for all contracts in contracts-bedrock to 1.0.0.

fix(ctb): missing FeeVault comments

feat(ctb): remove unnecessary ERC721 factory code

Add the `unsafeBlockSigner` to the specs for the
`SystemConfig` contract. This was overlooked when
the `unsafeBlockSigner` was added to the contract itself.

Fixes an incomplete comment in the SequencerFeeVault that was missing a
return.

gas snapshot

feat(ctb): receivedMessages => failedMessages

Removes a legacy getter that was mistakenly added to the ERC20 factory.
We never had a getter for the bridge variable.

Adds missing constructor comments in the FeeVault contracts.

Minor edit to a comment that had a typo in the CrossDomainMessenger.

First removes the legacy bridge and remoteChainId getter functions.
Since the ERC721 factory is being deployed at a new address, it's not
necessary to maintain ABI compatibility. We can safely remove these
functions. Also removes constructor checks that aren't really necessary
since we can always upgrade if needed and the odds of getting something
like that wrong don't seem significant enough to warrant extra code.

fix(ctp): Downgrade `contracts-bedrock` dep to fix CI