fix: improved error handling and build configuration in lib.rs

[DeVikingMark]

Description

This PR enhances the architecture and reliability of the build process in lib.rs:

• Added the ZKVM_TAG_VERSION constant for centralized management of the zkVM version.
• Introduced the BuildConfig structure for more flexible build process configuration.
• Improved error handling in build_zkvm_program using Result.
• Added informative error logging for zkVM program builds.
• Removed outdated commented-out code.

Motivation

• Improved code maintainability.
• More robust error handling.
• Simplified version update process.
• Adherence to Rust best practices.