fix(rpc): Make the verbose argument of the getrawtransaction RPC optional

[upbqdn]

Motivation

The verbose argument of the getrawtransaction RPC is specified as optional in the documentation: https://zcash.github.io/rpc/getrawtransaction.html. It's also specified as optional in Zebra's docs:

zebra/zebra-rpc/src/methods.rs

Line 215 in 5dd33d7

/// - `verbose`: (numeric, optional, default=0) If 0, return a string of hex-encoded data, otherwise return a JSON object.

, but not implemented as such.

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Specifications

https://zcash.github.io/rpc/getrawtransaction.html

Solution

• Use Option<u8> instead of u8 for the verbose argument.

Testing

• I adjusted existing tests and didn't add any new tests.
• I manually tested that the argument is optional with this PR and that its value defaults to 0.
• I also manually tested that Zebra required this argument without this PR, which didn't comply with the spec.

Review

Reviewer Checklist

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• Does the PR scope match the ticket?
• Are there enough tests to make sure it works? Do the tests cover the PR motivation?
• Are all the PR blockers dealt with?
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[teor2345]

Thanks!