Fix/xcframework modulemap collision

[Jevaites]

Summary

This PR prevents a SwiftPM/Xcode "Multiple commands produce …/include/module.modulemap" error that occurs when starknet.swift is used alongside other packages shipping an XCFramework with a top-level Headers/module.modulemap (e.g., swift-sodium).

Describe your changes

• For each slice of Frameworks/CryptoRs.xcframework:
  • Moved Headers/module.modulemap → Modules/module.modulemap.
  • Updated the module map to reference the header relative to its new location:

    module CryptoRs {
      header "../Headers/crypto-rs.h"
      export *
    }
    

  • (No API or Swift source changes.)

Linked issues

Closes #248

Breaking changes

• This issue contains breaking changes