feat(examples): add Base64 decoding async example

[Amit5601]

Motivation

The examples directory currently lacks a Base64 decoding implementation. Base64 is a highly common data encoding format in Web3 and cryptography, making it a valuable reference for developers learning how to serialize, deserialize, and process string data across the Host/Guest zkVM boundary.

Solution

Implemented an end-to-end Base64 decoding execution pipeline.

Implementation Details:

• Guest (program): Implemented standard Base64 decoding logic inside the zkVM, ensuring it successfully cross-compiles to the new riscv64im-succinct-zkvm-elf target.
• Host (script): Upgraded the host implementation to align with the latest async architecture, utilizing ProverClient::from_env().await, the updated ProvingKey verification traits, and the sp1_sdk::Elf::Static() wrapper.

Note on testing: The Rust logic and Host/Guest serialization compile flawlessly with 0 errors/warnings. My local hardware hits an OOM memory limit when attempting to generate the execution trace matrix locally via .execute() or .prove(), so I am relying on the CI/CD pipeline to generate the final execution/proof verification.

PR Checklist

• Added Tests (The example script serves as an end-to-end integration test)
• Added Documentation
• Breaking changes