engines: add zjs

[aneryu]

Summary

Adds zjs, a Zig rewrite of QuickJS, to the zoo.

• add Docker builds for amd64 and arm64
• teach the harness about console.log and zjs's -m module flag
• include the current conformance results and basic project metadata

Testing

• built, packaged, and smoke-tested zjs on arm64
• ran the complete build and script/module smoke tests on a native amd64 runner
• make -C engines/zjs conformance DIRECT=1 — 1,458/1,514 passed; the remaining 56 results are recorded in conformance.txt
• ran the Zoo test262 module smoke tests, including a module with a fixture dependency
• make -C harness all — 327 tests passed; mypy found no issues
• checked engine discovery, generated metadata, Dockerfile syntax, and git diff --check

The conformance results were generated with zjs commit 566d5d096d5feef5d4d7220a50dbec1f465b9148.