Refactor - Transaction Hash

[DaMatrix]

Description

This PR depends on #47 (bincode-2), #41 (macros), and #45 (crypto).

This adds a new struct type specific to transaction hashes. This brings three major advantages:

• Type-safety for all code interacting with transaction hashes
  • Has the added benefit of forcing all transaction hash objects to contain a valid transaction hash, whereas before there was no guarantee that the arbitrary Strings representing addresses were actually valid transaction hashes
• Improved performance: the transaction hash type wraps a fixed-length byte array, it causes no additional heap allocations and can be copied using just 2 instructions
• Compact binary serialization using Bincode 2

The new type is not actually used yet, but will be in subsequent PRs.

Changelog

• Added a dedicated type for transaction hashes
• Changed OutPoint's n from i32 to u32, as it can never be negative
• Implemented PlaceholderSeed for OutPoint and added a new constructor which takes a TxHash (this constructor will eventually become the default)

Type of Change

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• Bug fix
• New feature
• Enhancement or optimization
• Documentation update
• Other (please specify)

Checklist

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• I have tested the changes locally and they work as expected.
• I have added necessary documentation or updated existing documentation.
• My code follows the project's coding standards and style guidelines.
• I have added/updated relevant tests to ensure the changes are properly covered.
• I have checked for and resolved any merge conflicts.
• My commits have clear and descriptive messages.

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[BHouwens]

Same here as #52. These are potentially breaking so we need to be extremely thorough in testing