Harden flash crash runner with input validation and structured error handling

[Pushpenderrathore]

Summary

This improves the robustness and safety of the flash crash strategy runner by adding input validation and enhancing runtime error handling.

Changes

• Added strict private key format validation before bot initialization
• Improved CLI error handling with clearer user-facing messages
• Separated debug and non-debug logging behavior
• Added structured exception handling for async runtime
• Prevented cryptographic initialization errors from leaking stack traces in normal mode

Improvement

The previous implementation allowed cryptographic errors and stack traces to surface directly to the user, which reduced usability and made debugging less controlled. This update ensures:

• Fail-fast validation of critical configuration
• Cleaner CLI behavior
• More predictable runtime failure handling
• Improved developer debugging via --debug flag

Impact

No changes to trading logic.
Only improves CLI safety and reliability.

Testing

• Verified valid private key path works correctly
• Verified invalid key fails fast with clear message
• Verified debug mode prints full traceback
• Verified non-debug mode suppresses stack traces