feat(keyring-eth-money): remove signTransaction pass-through

[danroc]

Summary

• Remove signTransaction pass-through method from MoneyKeyring
• Unexport EvmSigner type and rename to MoneySigner; the type was incorrectly exported and no longer represents a full EVM signer
• Remove corresponding test
• Money accounts do not need to sign transactions

Changes

• BREAKING: MoneyKeyring.signTransaction is no longer available
• BREAKING: EvmSigner renamed to MoneySigner, no longer exported

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Note

Medium Risk
Breaking API surface change for consumers that previously called MoneyKeyring.signTransaction. Implementation changes are small and localized, but may require downstream updates and could affect runtime if callers still expect the method to exist.

Overview
Removes MoneyKeyring.signTransaction so Money accounts no longer expose transaction signing via the wrapped HdKeyring (breaking change).

Tightens the internal signer typing by unexporting/renaming EvmSigner to the non-exported MoneySigner (and dropping the transaction-signing method from that interface), deletes the corresponding unit test, and documents the breaking change in the changelog.

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