chore: move ulimit increase to per-step execution in CI workflows

[mrgrain]

Problem

The current CI workflow has separate ulimit increase steps, but ulimit changes don't persist across GitHub Actions steps. Each step runs in its own shell session, so the ulimit increase has no effect on subsequent test execution steps.

Changes

• Remove ineffective dedicated "Increase ulimit" steps from GitHub Actions workflows
• Move ulimit increase inline with test execution commands so it applies to the same shell session
• Apply ulimit only when running on macOS runners where it's needed

Validation

This change fixes the ulimit configuration that was previously ineffective. The ulimit increase now actually applies to the test execution since it runs in the same shell session.

Checklist

• If this PR includes a functional change to the runtime behavior of the code, I have added or updated automated test coverage for this change.
• If this PR requires a change to the Project Architecture README, I have included that update in this PR.
• If this PR requires a docs update, I have linked to that docs PR above.
• If this PR modifies E2E tests, makes changes to resource provisioning, or makes SDK calls, I have run the PR checks with the run-e2e label set.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

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Latest commit: 0db8fe2

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