Import a module generated by a repo's host tool

[godofecht]

What

Adds a gen_imports list to #Module. Each entry declares a host tool (tool_root, tool_name), an ordered argument list (each arg is literal, input_file, or output_file), and which output_file becomes the generated module's root. Azazel builds the tool for b.graph.host, runs it (addFileArg for inputs, addOutputFileArg for outputs), and imports the captured output path under alias.

Why

Some repos generate a source module at build time by compiling a host tool, running it, and importing the file it writes. zls is the motivating case: build.zig compiles src/tools/config_gen.zig, runs it with the langref as input, and imports the emitted version_data.zig as the version_data module. Azazel modeled package and generated options but had no codegen-to-module primitive, so any module importing a generated module could not be built from the CUE model alone.

How it flows

• schema.cue: #GenArg + #GeneratedImport, and gen_imports on #Module.
• gen_build_spec.sh: GenArg / GeneratedImport structs + emitter.
• build.zig: generatedModule builds the host tool, runs it capturing each output file's LazyPath, and returns a module over the one named by output. Wired into the module loop alongside pkg_imports.
• build_spec_test.zig: shape assertions (tool_root ends in .zig; the named output is one of the output_file args).

Verification

Built a probe against zls's real config_gen on the mach 0.17 toolchain: Azazel compiles the tool, runs it to emit the 2456-line version_data.zig, and the probe imports and references its builtins map, then runs. Azazel's own build and the 23 spec tests pass on 0.14.1 / 0.15.2 / 0.16.0 (b.graph.host and single_threaded compile on all three).