Standardize Package Release Fetching Format and Implement JSON API for Python

[kbukum1]

What are you trying to accomplish?

This PR standardizes the format for package release fetching by introducing a common structure (PackageRelease, PackageLanguage, PackageDetails) that ensures consistency across ecosystems. This standardized format will be applicable to other package managers in the future.

As the first step, it applies this standardized fetching format to Python, implementing JSON API fetching as the primary method while keeping HTML fallback support for backward compatibility.

The JSON API fetching is behind a feature flag to ensure a controlled rollout and allow for further validation before full adoption.

Switching to JSON API fetching provides the following benefits:

1. Efficiency – JSON API fetching is faster and more structured compared to HTML parsing.
2. More metadata – JSON API provides release dates, which were not available in the HTML-based approach.
   • Release dates are crucial for the upcoming cooldown feature, which will rely on this metadata to determine update timing.

What does this PR do?

• Standardizes package release fetching format, introducing PackageRelease, PackageLanguage, and PackageDetails as common data structures.
• Implements JSON API fetching ({url}/pypi) behind a feature flag, allowing for controlled testing and gradual rollout.
• Includes release dates in package metadata, supporting future cooldown logic.
• Maintains HTML-based fallback fetching to support cases where the JSON API is unavailable or the feature flag is disabled.
• Ensures consistency, maintainability, and extensibility for future ecosystem integrations.

Anything you want to highlight for special attention from reviewers?

• Ensure that the new standardized fetching format (PackageRelease, PackageLanguage, PackageDetails) is correctly applied to Python.
• Confirm that JSON API fetching works correctly when the feature flag is enabled.
• Verify that fallback to HTML parsing works as expected when JSON API is unavailable or the feature flag is disabled.
• Check that release date metadata is correctly included and will be usable for cooldown logic.
• Validate that existing package fetching behavior remains unchanged functionally when the feature flag is off.

How will you know you've accomplished your goal?

• Python package fetching uses the standardized format (PackageRelease, PackageLanguage, PackageDetails).
• JSON API fetching provides release dates, improving metadata quality and enabling cooldown logic.
• When the feature flag is disabled, the system falls back to HTML fetching, ensuring no functional regressions.
• Performance improves due to more efficient JSON API fetching compared to HTML parsing.
• Standardization makes it easier to extend package release fetching to other ecosystems.
• All test cases pass, validating that both JSON and HTML metadata fetching work reliably.

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Checklist ✅

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including additional test cases for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[randhircs]

I approve it, Tests cases are updated and I assume we have added all the test cases in terms of validating/verifying json response date.