Add remaining detector and vulnerability documentation

[arturoBeccar]

Description

For every added vulnerability class and detector, add or update corresponding documentation. The list of remaining detectors is:

• - avoid-panic-error
• - avoid-unsafe-block
• - dos-unbounded-operation
• - soroban-version

Acceptance Criteria

• Add an entry in Vulnerability Classes section of the Test Cases readme.
• Add a readme file within /detectors with detector documentation.
• Add newline with detector to Detectors table in main README.md

Estimate

1