chore: add license IDs

[horsefacts]

Motivation

A few contracts are missing SPDX license IDs.

Merge Checklist

Choose all relevant options below by adding an x now or at any time before submitting for review

• [x] The PR title adheres to the conventional commits standard
• [x] The PR has been tagged with change type label(s) (i.e. documentation, feature, bugfix, or chore)
• [x] The PR's changes adhere to all the requirements in the contribution guidelines
• [x] All commits have been signed

---

PR-Codex overview

Focus of this PR:

This PR focuses on adding SPDX-License-Identifier to the Solidity files and making import statements more explicit.

Detailed summary:

• Added SPDX-License-Identifier to the Solidity files.
• Made import statements more explicit by specifying the exact file paths.
• Updated the pragma version of some Solidity files.
• Added a new library TransferHelper in the lib directory.
• Added a new interface IBundler in the interfaces directory.
• Added a new interface IMetadataValidator in the interfaces directory.
• Added a new interface IKeyRegistry in the interfaces directory.
• Added a new library EIP712 in the lib directory.
• Added a new validator SignedKeyRequestValidator in the validators directory.
• Added a new interface IStorageRegistry in the interfaces directory.
• Added a new library Signatures in the lib directory.

✨ Ask PR-Codex anything about this PR by commenting with /codex {your question}

[github-actions[bot]]

Coverage after merging horsefacts/bundler-license-id into main will be

98.66%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
Bundler.sol	100%	100%	100%	100%
FnameResolver.sol	100%	100%	100%	100%
IdRegistry.sol	100%	100%	100%	100%
KeyRegistry.sol	100%	100%	100%	100%
RecoveryProxy.sol	100%	100%	100%	100%
StorageRegistry.sol	100%	100%	100%	100%
src/lib
EIP712.sol	50%	100%	50%	50%	19
Signatures.sol	100%	100%	100%	100%
TransferHelper.sol	0%	0%	0%	0%	12, 17, 20, 20, 20
TrustedCaller.sol	100%	100%	100%	100%
src/validators
SignedKeyRequestValidator.sol	100%	100%	100%	100%