Avoid displaying unverified PSBT fees

[Jacksper13]

Summary

• cross-check witness_utxo against the hash-verified previous transaction when both PSBT fields are present
• mark fees as unverified when collaborative inputs provide only unbound witness amounts
• suppress misleading percentage warnings and display an explicit unverified-fee warning
• preserve existing SegWit classification, history-cache, and serialization behavior
• add parser, fee-policy, history-cache, and review-rendering regression coverage

Impact

Ordinary single-wallet SegWit transactions continue to display their network fee. Witness-only amounts for inputs Passport will sign retain the existing numeric display because the signature commits to that input amount and the history cache detects changed amounts across signing attempts.

Collaborative transactions whose external input amounts cannot be independently checked now identify the fee as unverified instead of displaying an attacker-controlled value.

Testing

• focused PSBT fee unit script under CPython with MicroPython compatibility stubs
• python -m py_compile on changed Python files
• python -m pycodestyle on changed Python files
• python -m reuse lint-file ports/stm32/boards/Passport/modules/tests/unit/psbt_fee.py
• git diff --check

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