Move polyglot SDK validation tests to CLI E2E test infrastructure

[davidfowl]

Problem

The polyglot SDK validation tests (.github/workflows/polyglot-validation.yml) run as standalone Docker builds in CI. These tests are fragile because they build Docker images that run apt-get and curl against external package mirrors, which frequently fail with transient errors (504s, digest mismatches, timeouts).

Example failure from https://github.com/microsoft/aspire/actions/runs/24609589983/job/71961739197:

#8 0.165 curl: (22) The requested URL returned error: 504
Process completed with exit code 4.

These tests consistently fail across unrelated PRs due to infrastructure issues, blocking merges.

Proposal

Move the polyglot SDK validation tests (Python, Java, Go, Rust, TypeScript) to the CLI E2E test infrastructure (Aspire.Cli.EndToEnd.Tests). This would:

• Use the existing Hex1b terminal automation for consistent test execution
• Share the CLI E2E Docker base image instead of building separate images per language
• Benefit from retry logic and better error reporting in the E2E framework
• Reduce CI flakiness from transient network failures during Docker builds
• Align with how other CLI-driven tests are structured