Fix SPM: point root Package.swift binaryTargets to 4.7.3 release

[LeeeeSuHyeon]

Description

The committed root Package.swift has been stale for ~1 year and still pins its binaryTarget URLs/checksums to the 4.2.9 release. Because SPM reads the manifest committed in the checked-out tree (not the Package.swift published as a release asset), every SPM consumer links the 4.2.9 binary regardless of the resolved version — so APIs added after 4.2.9 (e.g. TronSigningInput.rawJson, RippleSigningInput.rawJson) are missing at compile time even though Package.resolved shows a newer version.

This PR updates the committed root Package.swift to the 4.7.3 artifacts, matching the correct Package.swift already shipped as the 4.7.3 release asset:

• WalletCore → releases/download/4.7.3/WalletCore.xcframework.zip (checksum 179b1276…)
• WalletCoreSwiftProtobuf → releases/download/4.7.3/WalletCoreSwiftProtobuf.xcframework.zip (checksum 875e4d9f…)

This also fixes the outdated Protobuf artifact name (SwiftProtobuf.xcframework.zip → WalletCoreSwiftProtobuf.xcframework.zip).

Fixes #4846

Note: this is the minimal fix to unblock SPM users. Longer term, the release automation should regenerate and commit this manifest into the tree on each release so it can't drift again.

How to test

1. Point an SPM project at this branch:

   .package(url: "https://github.com/<fork>/wallet-core", branch: "fix/spm-package-manifest")
   

2. Resolve packages, then confirm a post-4.2.9 API now compiles:

   _ = TronSigningInput.with  { $0.rawJson = "" }
   _ = RippleSigningInput.with { $0.rawJson = "" }
   

   (These fail to compile against the current master, which links 4.2.9.)

3. Optionally verify the checksums match the published 4.7.3 assets:

   curl -sL -o WalletCore.xcframework.zip \
     https://github.com/trustwallet/wallet-core/releases/download/4.7.3/WalletCore.xcframework.zip
   swift package compute-checksum WalletCore.xcframework.zip
   # → 179b12764383479fe8ab02689872113ebdfcf923ca96896c133a31e516b038dc
   

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist

• Create pull request as draft initially, unless its complete.
• Add tests to cover changes as needed.
• Update documentation as needed.
• If there is a related Issue, mention it in the description.

If you're adding a new blockchain

• I have read the guidelines for adding a new blockchain.