chore(entrypoint): enhance logging and add documentation

[techvoyagerX]

Description

This PR improves the entrypoint.rs file by adding better logging, error handling, and documentation. The changes aim to make the code more maintainable, improve debugging efficiency, and enhance readability for new contributors.

Changes Made

• Added msg! logs to display:
  • The program ID being executed.
  • The number of accounts passed to the entrypoint.
• Included context-specific messages before printing errors for better debugging context.
• Added detailed comments to:
  • Explain the process_instruction function's purpose.
  • Describe the parameters and return value.