refactor(keyring-api): make capabilities boolean fields exact optionals

[ccharly]

To avoid having to update every keyrings after we add a new capability.

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Note

Medium Risk
Moderate risk because it changes the validation/typing contract for KeyringCapabilities.bip44 and updates multiple keyring wrappers/tests; consumers that relied on explicit false values may need to treat missing fields as unsupported.

Overview
Makes BIP-44 capability flags optional in KeyringCapabilities. The KeyringCapabilitiesStruct now treats bip44.derivePath, deriveIndex, deriveIndexRange, and discover as exactOptional(boolean()), so keyrings can omit unsupported capabilities instead of setting them to false.

Updates Ethereum keyring wrappers (HD/Ledger/QR/Trezor) and their tests to stop emitting/asserting false for unsupported BIP-44 capabilities, and documents the new semantics in the keyring-api changelog (and references the PR in downstream package changelogs).

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