Add DoubleNestedMultisigBuilder script contract

[jackchuma]

Adds a double nested multisig builder script for signing tasks where there is an extra layer of multisig nesting.

There are three safe types involved in a double nested multisig:

1. The top-level safe, which should be returned by _ownerSafe().
2. One or more intermediate safes, which are signers for the top-level safe.
3. Signer safes, which are signers for the intermediate safes. There should be at least one signer safe per intermediate safe.

[cb-heimdall]

✅ Heimdall Review Status

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[cb-heimdall]

Review Error for MrSaints @ 2025-01-15 20:15:46 UTC
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