refactor: rename crate hudi-tests to hudi-test

[xushiyan]

Description

"tests" can imply containing test cases. Rename hudi-tests to hudi-test to avoid potential confusion.

Replace custom maintained assert_not! with standard lib macro assert!. And remove unused macro assert_approx_eq!.

How are the changes test-covered

• N/A
• Automated tests (unit and/or integration tests)
• Manual tests
  • Details are described below

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.20%. Comparing base (f722508) to head (d450516).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #262   +/-   ##
=======================================
  Coverage   91.20%   91.20%           
=======================================
  Files          40       40           
  Lines        1967     1967           
=======================================
  Hits         1794     1794           
  Misses        173      173           

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