feat: adds webauthn account

[linnall]

Pull Request Checklist

• Did you add new tests and confirm existing tests pass? (yarn test)
• Did you update relevant docs? (docs are found in the site folder, and guidelines for updating/adding docs can be found in the contribution guide)
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PR-Codex overview

This PR introduces support for a new account type, ModularAccountV2NoSigner, which allows operations without a signer, specifically for the webauthn mode. It modifies the createMAv2Base and createModularAccountV2 functions to accommodate these changes.

Detailed summary

• Added ModularAccountV2NoSigner type for accounts without a signer.
• Updated createMAv2Base to handle configurations with and without a signer.
• Introduced CreateModularAccountV2ParamsNoSigner type for webauthn mode.
• Enhanced createModularAccountV2 to accept both signer and no-signer configurations.
• Implemented logic for handling webauthn parameters and account initialization.

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