Implement SignAllTransactions Method Across All Wallet Integrations in Solana.Unity-SDK

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Is your feature request related to a problem? Please describe.
Yes, the SignAllTransactions method is currently unimplemented across almost all wallet integrations in the Solana.Unity-SDK. This lack of implementation creates a significant gap for developers who need to sign multiple transactions at once. It forces manual handling of this process, leading to inefficiencies, increased complexity, and potential errors.

Describe the solution you'd like
I would like to see the SignAllTransactions method fully implemented across all supported wallet integrations (WebGL, mobile, etc.). This solution should include:

• Batch transaction signing functionality.
• Signature deduplication, prioritizing non-empty signatures.
• Full support for VersionedTransaction and Transaction deserialization to ensure compatibility across different transaction types in Solana.

Describe alternatives you've considered
One alternative we are considering is switching to an updated fork of the SDK that includes these changes. This would allow us to bypass the limitations of the current version and use a more up-to-date version with the necessary transaction signing functionality in place.

Another alternative would be to manually implement the signing logic for multiple transactions, but this would be inefficient and would not scale well for complex use cases.

Additional context
The absence of this feature significantly limits the utility of the SDK for handling multiple transactions. Additionally, this issue could be an opportunity to clean up outdated integrations, such as the deprecated Phantom WebGL support, and focus on implementing key features for wallets that are actively maintained. Moving forward, either enhancing this functionality within the SDK or adopting a better-maintained fork will be essential.