Support for ISRC6 (__validate__ & __execute__ ) etc.

[remollemo]

1. Support for ISRC6 (validate & execute )
2. Refactor test and test utils.
3. Generate test.cairo signature via python script (directly).
4. send_tx.py utility to prepare (EFO) for starkly and send tx (normal tx) via rpc.

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Note

High Risk
Touches core account entrypoints (__validate__/__execute__) and EIP-712 hashing/signature verification, so any mismatch can break transaction validity or execution restrictions.

Overview
Implements ISRC6 on StarknetEth712Account by adding __validate__ (EIP-712 secp256k1 signature check over a new Transaction struct) and __execute__ (protocol-only caller + tx version gating, executing calls individually), and registers ISRC6_ID during initialization.

Extends eth_712_utils.cairo with EIP-712 hashing for InvokeV3 transactions (TransactionMetadata/Transaction, get_transaction_hash), tx version validation, resource-bounds serialization, and a flexible signature parser for is_valid_signature (accepts 5 or 6 felts).

Refactors tests to use fixed deployment addresses for stable precomputed signatures, adds coverage for ISRC6 signature validation, __validate__/__execute__ flows, upgrade via both EFO and regular tx, and enforces signature length checks. Script-side, introduces shared Python EIP-712 hashing (scripts/eip712.py), an idempotent signature generator that rewrites test_utils.cairo between markers, and a new send_tx.py utility to sign/send InvokeV3 or print EFO calldata; updates script dependencies and adds an example calls JSON.

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[remollemo]

@remollemo reviewed 9 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on ItayRosenberg).