PY-86778 [python] Migrate Python test environments from local builds to prebuilt standalone distributions

Replace Gradle-based local Python compilation with prebuilt standalone distributions
downloaded from JetBrains cache redirector. Introduces provider-based architecture
for test environment management with improved JUnit4/JUnit5 integration.

Key changes:
- Remove setup-test-environment Gradle module and build infrastructure
- Introduce python-test-env modules (core, common, plain, conda, uv, junit4, junit5)
- Implement PyEnvironmentProvider/PyEnvironmentSpec abstractions
- Add JUnit5 annotations (@RequiresPoetry, @RequiresUv, @RunOnEnvironments)
- Implement caching system with PyEnvDownloadCache and variant-specific directories
- Predefined environments like: VANILLA_2_7, VANILLA_3_11, VANILLA_3_12, VANILLA_3_13

Benefits:
- Faster test environment provisioning (no compilation required)
- Consistent cross-platform behavior with identical Python builds
- Improved reliability by eliminating platform-specific build failures
- Better test framework integration with parameterized environment testing

GitOrigin-RevId: a44957c3014f9e1fc7dbec347a7e245675f999c1

python/python-exec-service/execService.python/intellij.python.community.execService.python.iml

@@ -5,7 +5,6 @@
     <content url="file://$MODULE_DIR$">
       <sourceFolder url="file://$MODULE_DIR$/resources" type="java-resource" />
       <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" packagePrefix="com.intellij.python.community.execService.python" />
-      <sourceFolder url="file://$MODULE_DIR$/tests" isTestSource="true" />
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />