Fix BEEF validation issues and refactor validation logic (#211, #96)

[shruggr]

Description

This PR fixes multiple BEEF-related issues:

1. Non-deterministic BEEF validation ([BUG] BEEF IsValid/Verify algorithm is unstable - gives different results for the same input BEEF #211)
2. BEEF parsing panic with "no leaves at height" error ([BUG]There are no leaves at height: ... #96)
3. Incorrect validation logic for transactions in BUMPs
4. Confusing method name SortTxs

Root Cause Analysis

Issue #211: The validation logic was not properly handling transaction validation order, causing non-deterministic results.

Issue #96: The SDK was being too strict during BEEF parsing, panicking when transactions didn't have merkle paths or source transactions. This is valid BEEF data that should be handled gracefully.

Validation Logic: The validation wasn't properly checking if transactions appear in BUMPs (have proof) for all DataFormat types.

Solutions

1. Fixed validation order by ensuring transactions with merkle paths are added to the valid set before validating dependent transactions

2. Removed panic during parsing - transactions without merkle paths or source transactions are now handled gracefully

3. Refactored validation logic:

   • Renamed SortTxs() to ValidateTransactions() for clarity
   • Added proper validation for TxIDOnly and RawTx formats by checking if they appear in BUMPs
   • Added verification that RawTxAndBumpIndex has accurate bump index
   • Returns a structured ValidationResult with categorized transaction lists

4. Fixed test assumptions that incorrectly expected all input transactions to be present in BEEF

5. Performance optimization:

   • Refactored BEEF implementation to use chainhash.Hash directly as map keys instead of string conversions
   • Added *ByHash method variants to avoid unnecessary hash/string conversions
   • Updated collectAncestors to return []chainhash.Hash instead of []string

Additional Fixes

• Fixed README installation instructions to use go get instead of go install ([BUG] install cmd on readme does not work, replace with go get #202)

Testing

• Added test cases from issues [BUG] BEEF IsValid/Verify algorithm is unstable - gives different results for the same input BEEF #211 and [BUG]There are no leaves at height: ... #96
• Fixed existing tests to work with new validation logic
• All tests pass consistently with proper validation behavior
• No existing functionality was broken

Changes

• Modified verifyValid() to use new ValidateTransactions() method
• Added ValidateTransactions() method with comprehensive validation logic
• Removed panic in readAllTransactions() for missing source transactions
• Updated all test references from SortTxs to ValidateTransactions
• Fixed test in TestBeefGetValidTxids to handle transactions with merkle paths correctly
• Refactored internal BEEF structures to use chainhash.Hash for better performance

Fixes #211
Fixes #96
Fixes #202

[kuba-4chain]

Hey, I just added a similar fix here:
#213

I did not see you've already pushed the fix, you beat me to it 😄 I'll close my PR as a duplicate.

There's just one thing, I think that the b.SortTxs() function at the beginning of the verifyValid method is unnecessary and could be removed, as it doesn't sort in-place, if I understand this correctly.

Other than that, thanks for the fix!

[rohenaz]

lgtm