feat: add OWS (Open Wallet Standard) as wallet signer

[kevarifin14]

Summary

Adds --ows <WALLET> flag for loading signers from an OWS encrypted vault, alongside the existing --ledger, --trezor, --aws, --gcp, and --turnkey options. Feature-gated behind ows.

Usage

# Before: Foundry-specific keystore or raw key
cast send <TO> --value 1ether --account my-wallet
cast send <TO> --value 1ether --private-key 0x...

# After: OWS encrypted vault (same vault as Solana CLI, Tempo, etc.)
cast send <TO> --value 1ether --ows my-wallet
forge script Deploy.s.sol --ows my-wallet

One wallet created with ows wallet create works in cast, forge, solana, tempo, polymarket — every tool.

Changes

File	What
crates/wallets/src/opts.rs	Added --ows flag, resolution in maybe_signer()
crates/wallets/src/signer.rs	Added WalletSigner::from_ows()
crates/wallets/src/error.rs	Added ows_unsupported() helper

Feature-gated: --features ows. Follows the same pattern as --aws, --gcp, --turnkey.

How it works

OWS decrypts the EVM signing key from the vault (AES-256-GCM, scrypt KDF) and wraps it as a PrivateKeySigner. The key is only in memory during signing, then wiped. No plaintext on disk.

Dependencies

Would require adding ows-lib and ows-core as optional dependencies to foundry-wallets.