Rename MariaDB task table state enum definitions for consistency

[coderabbitai]

Problem

There is an inconsistency between the Python task state string representations and what would be more standard naming:

Current Python representations:

• TaskState.Succeeded → "success"
• TaskState.Failed → "fail"
• TaskState.Cancelled → "cancel"

Suggested consistent representations:

• TaskState.Succeeded → "succeeded"
• TaskState.Failed → "failed"
• TaskState.Cancelled → "cancelled"

Impact

This change requires updates to both:

• C++ codebase (MariaDB table definitions)
• Python codebase (string mapping)

Context

This issue was identified during code review of PR #216 where the task state string mappings were introduced.

Backlinks:

• PR: feat(spider-py): Add job submission support for MariaDB storage backend. #216
• Comment: feat(spider-py): Add job submission support for MariaDB storage backend. #216 (comment)
• Requested by: @sitaowang1998