Improve test suite: increase coverage and reduce total execution time

[vdusek]

Summary

Umbrella issue tracking improvements to the test suite — adding new tests, restructuring existing ones, increasing code coverage, and reducing execution time.

Related PRs

• test: split integration tests into integration and e2e suites #781 — Split integration tests into integration and e2e suites
  Separates Actor-based tests (build & deploy on Apify platform) into a dedicated tests/e2e/ directory. Adds e2e-tests poe task and CI job. Gives a clearer separation between local integration tests and platform e2e tests.

• test: Increase total test coverage and reduce E2E tests #783 — Increase total test coverage and reduce E2E tests
  Reduces expensive e2e tests from 65 to 37 (-43%) by migrating storage/SDK-logic tests to integration and unit tiers. Adds 90+ new unit tests. Coverage increased from 81.86% to 85.49%. Total execution time reduced by ~50%.

• test: add e2e tests for Crawlee crawlers as Apify Actors #784 — Add e2e tests for Crawlee crawlers as Apify Actors
  Adds 6 e2e tests verifying each Crawlee crawler type (BasicCrawler, HttpCrawler, BeautifulSoupCrawler, ParselCrawler, PlaywrightCrawler, AdaptivePlaywrightCrawler) works correctly when deployed as an Actor.

• apify/apify-core#25840 — Increase limits of Python SDK service account
  Increases platform limits for the test service account to support the expanded test suite.