(6/17) Creates `XRPDepositPreauth` Protobuf Wrapper Class

[amiecorso]

High Level Overview of Change

This PR implements the class XRPDepositPreauth - a native Swift struct to wrap the DepositPreauth protocol buffer. See also https://xrpl.org/depositpreauth.html

Context of Change

Effort to implement additional XRPL transaction types beyond Payment in the SDK.

Type of Change

• [x] New feature (non-breaking change which adds functionality)
• [x] Tests (You added tests for code that already exists, or your new feature included in this PR)

Before / After

XRPDepositPreauth class and conversion unit tests now exist.

Test Plan

Unit tests added to verify conversion. CI passes.

Future Tasks

[codecov[bot]]

Codecov Report

Merging #275 into master will increase coverage by 0.28%. The diff coverage is 96.36%.

@@            Coverage Diff             @@
##           master     #275      +/-   ##
==========================================
+ Coverage   90.40%   90.68%   +0.28%     
==========================================
  Files          48       51       +3     
  Lines        1105     1160      +55     
==========================================
+ Hits          999     1052      +53     
- Misses        106      108       +2     

Impacted Files	Coverage Δ
...Model/XRPCheckCash+Org_Xrpl_Rpc_V1_CheckCash.swift	93.33% <93.33%> (ø)
...l/XRPCheckCreate+Org_Xrpl_Rpc_V1_CheckCreate.swift	95.83% <95.83%> (ø)
...epositPreauth+Org_Xrpl_Rpc_V1_DepositPreauth.swift	100.00% <100.00%> (ø)

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