fix: raise ValueError with context on malformed signed URL

[tempoo04]

What does this PR do?

Fixes a brittle URL parsing pattern in InferenceModel.predict_video() where splitting the signed URL to extract the
expiry value would raise a bare IndexError with no context if the URL format ever changes or is unexpected.

Before:

signed_url_expires = signed_url.split("&X-Goog-Expires")[1].split("&")[0].strip("=")

After:

try:
    signed_url_expires = signed_url.split("&X-Goog-Expires")[1].split("&")[0].strip("=")
except IndexError as e:
    raise ValueError(f"Could not parse expiry from signed URL: {signed_url}") from e

Related Issue(s): N/A

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Testing

• I have tested this change locally
• I have added/updated tests for this change

Test details:
No behavioral change for valid URLs. Verified the error path raises ValueError with a descriptive message instead of a
bare IndexError.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings or errors

Additional Context

A bare IndexError gives no indication of what failed or what the URL looked like. The fix wraps the parse in a
try/except and re-raises as ValueError with the offending URL in the message, making debugging significantly faster.