Fix issue 110

[KXYWISE]

Closes #110
I have documented all variants in the ScoutAccessError enum with doc comments and updated the error codes table in the README.md to reflect the complete set of errors.

1. Documentation in contracts/scout_access/src/errors.rs: Added /// doc comments for every variant in ScoutAccessError.
2. Updated README.md: Cleaned up the Error Codes table to correctly reflect the variants present in ScoutAccessError, ensuring accurate descriptions, common causes, and resolutions.
3. Verification: Ran cargo doc --no-deps -p scoutchain-scout-access which succeeded, confirming that the new documentation is correctly picked up by the Rust doc generator.

The error table in README.md now provides a consistent and accurate reference for developers.

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