feat: migrate Django 5.2 upgrade and 3.2/4.2 deprecations

[sinhasubham]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request updates the Spanner database backend to support Django 5.2 and Python 3.10+, while removing legacy support for Django 3.2 and 4.2. Key changes include the implementation of a global client cache to prevent initialization crashes, support for JSONArray, GeneratedField, and db_default, and a retry mechanism for flushing tables with foreign key constraints. Feedback highlights several critical issues: the use of a 32-bit mask for primary key generation significantly reduces the key space, and making GOOGLE_CLOUD_PROJECT mandatory is a breaking change for local development. Additionally, the package version was incorrectly decremented, and a minor version bump was recommended for this release. Finally, using WHERE 1=1 was suggested as a more idiomatic alternative to WHERE true for flush operations.