feat: Add multi-arch platform support for container builds

[munishchouhan]

Summary

• Add support for multi-arch container builds via --platform linux/amd64,linux/arm64 or the shorthand --platform all
• Platform values are normalized to canonical form (e.g., x86_64 → linux/amd64), with whitespace trimming and deduplication
• Multi-arch builds are validated to require a containerfile or package spec, and are incompatible with Singularity format

Test plan

• Single platform aliases normalize correctly (amd64 → linux/amd64, x86_64 → linux/amd64, etc.)
• Comma-separated platforms normalize and deduplicate (amd64,arm64 → linux/amd64,linux/arm64)
• --platform all expands to linux/amd64,linux/arm64
• Multi-arch with containerfile or conda packages succeeds
• Multi-arch with image-only (no containerfile) fails with clear error
• Multi-arch + --singularity fails with clear error (both comma-separated and all)
• Invalid platform in comma-separated list fails with clear error
• Whitespace in comma-separated values handled correctly
• Duplicate platforms deduplicated
• All 118 tests pass

Files changed

• App.java (+47/-5) — platform normalization, canonicalization, multi-arch validation
• AppTest.groovy (+263/-12) — 12 new test cases, updated existing platform test to verify canonical form

[munishchouhan]

tested:

% /Users/munish.chouhan/testing_ground/wave-cli/app/build/native/nativeCompile/wave --conda-package numpy --platform all --wave-endpoint http://localhost:9090
munish-wave.seqera.dev/wt/25e31947a8f2/hrma017/dev/numpy:numpy--fed0cf6df860f9d0

[jonmarti]

LGTM, minor comment left

[pditommaso]

Thanks folks, I had already an implementation for this. Closing in favour of #107