feat: Glia import path — (import "foo") for .glia scripts

[lthibault]

Parent

Part of #272 (Glia import system)

Summary

Implement the Glia-script import path: (import "foo") resolves /lib/foo.glia from the merged FHS image, evals it in an isolated Env, and binds all top-level defs into the caller's Env with a foo/ prefix.

Scope

• Add Expr::Import variant to crates/glia/src/expr.rs (match arm in analyze_list())
• Create crates/glia/src/import.rs with resolution pipeline
• Resolution order: search /lib/{name}.glia first, then /lib/{name}.wasm
• Eval imported .glia in fresh Env (isolated — no leaking unprefixed defs)
• Bind results as {module}/ prefixed names in caller's root frame via set_root()
• Support absolute /ipfs/-prefixed paths: (import "/ipfs/QmHash.../foo.glia")
• Circular import detection via HashSet<String> threaded through eval

Non-goals

• WASM imports (see sibling issue)
• Import caching / idempotent require (see TODOS.md)
• Guard clauses, namespace objects

Test cases (from design doc)

• (import "utils") → utils/helper-fn callable
• Isolated eval: imported defs don't leak unprefixed into caller
• Module not found → error
• Empty .glia file → no bindings, no error
• Parse error in imported file → propagated error
• Nested path: (import "math/core") → /lib/math/core.glia
• Circular import detection
• /ipfs/-prefixed absolute import

Dependencies

• None (pure Glia-side work, uses existing WASI fs)