[WIP] Update comment for P2TR support in PSBT

[Codex]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>This comment says “P2TR aren't supported yet”, but PSBT parsing/building currently has a P2TR branch (key-path) in UtxoPsbt and the tx builder supports P2TR key-path spending. Please update the comment to reflect the actual limitation (e.g., P2WSH is unsupported; P2TR script-path is unsupported) so the test doesn’t mislead future readers.</issue_title>
<issue_description>This comment says “P2TR aren't supported yet”, but PSBT parsing/building currently has a P2TR branch (key-path) in UtxoPsbt and the tx builder supports P2TR key-path spending. Please update the comment to reflect the actual limitation (e.g., P2WSH is unsupported; P2TR script-path is unsupported) so the test doesn’t mislead future readers.

    // because `witness_utxo` must contain a supported witness UTXO type (currently P2WPKH in this test path). Please note that `P2WSH` and `P2TR` script-path are not supported yet.

Originally posted by @copilot-pull-request-reviewer in trustwallet#4749 (comment)</issue_description>

• Closes This comment says “P2TR aren't supported yet”, but PSBT parsing/building currently has a P2TR branch (key-path) in UtxoPsbt and the tx builder supports P2TR key-path spending. Please update the comment to reflect the actual limitation (e.g., P2WSH is unsupported; P2TR *script-path* is unsupported) so the test doesn’t mislead future readers. #4

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