feat: configurable e2e test cases

[anna-singleton-resolver]

We should allow users of the client library to select which e2e test cases are runnable. This would allow us to easily run the benign cases as well as the live ones, to make the e2e cases useful against development environments which do not have access to the live versions of the classifiers

[Copilot]

Pull request overview

Adds environment-driven selection of end-to-end (E2E) test case sets so the E2E classifier test can be run against different testcase directories without code changes.

Changes:

• Introduce load_test_cases_by_env() to select the testcase directory via ATHENA_E2E_TESTCASE_DIR (defaulting to integrator_sample).
• Update test_classify_single to use the new env-based loader instead of a hard-coded testcase directory.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
tests/functional/e2e/testcases/parser.py	Adds an env-based testcase loader wrapper around load_test_cases().
tests/functional/e2e/test_classify_single.py	Switches testcase initialization to use the env-based loader.

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[anna-singleton-resolver]

superseded by #117 , PR is no longer necessary