chore(release): prepare Python SDK 1.5.8

[YiChengZQZ]

Summary

• Bump global-open-sdk-python from 1.5.7 to 1.5.8.
• Prepare the merged Payment Hold/Release API updates for publication.

Validation

• Post-merge release regression: Offline 18/18 and Sandbox 5/5 passed.
• Wheel and sdist builds passed twine checks.
• Both artifacts installed successfully in isolated environments.
• Version, User-Agent, and new Hold/Release imports were verified.
• Git, wheel, and sdist case-collision checks passed.

Scope

This PR changes only the SDK version source and README version example.