feat(js): export module/namespace consts and enums

[nazarhussain]

Motivation

While porting @chainsafe/swap-or-not-shuffle into lodestar-z (ChainSafe/lodestar-z#559), scalar pub const decls and enums inside exported modules were silently skipped by js.exportModule's reflection — the binding had to assign constants like SHUFFLE_ROUNDS_MAINNET and ByteCount on the JS side. Classes already auto-export such consts as statics (applyStaticFields); this extends the same behavior to namespaces and the module root.

Changes

• Const export: scalar/string pub const decls (int, float, bool, []const u8, string literals) export as enumerable value properties at the module root and inside namespaces, reusing wrap_class.isStaticValueType/createStaticFieldValue (now pub). A namespace containing only consts now exports too.
• Enum export: pub const X = enum {...} exports as a frozen plain object mapping each tag name (verbatim, no case conversion) to its integer value, mirroring napi-rs #[napi] pub enum. Signed tag values preserved.
• Docs: TypedArray.fromExternal doc now states it copies (pointing at OwnedTypedArray.fromOwnedSlice/intoValue for ownership transfer) and warns it panics outside DSL callbacks. New README "Constants and Enums" section.

Decisions

• Consts are enumerable (setNamedProperty), matching namespace function properties. Verified class statics are also enumerable, so the two paths are consistent.
• Enum objects are frozen — safer semantics for constants; napi-rs leaves them mutable.
• Other const shapes (struct values, arrays) remain skipped; the .register hook stays the escape hatch.

Testing

10 new vitest cases in examples/js_dsl (root/namespace consts, const-only namespace, enumerability, verbatim enum tags, signed values, frozen-object semantics), written first and watched fail. Full suite: zig build test:zapi + 130 vitest tests green.

Consumer cleanup

Once released, lodestar-z deletes its bindings.js constant assignments and declares the consts/enum in bindings/napi/shuffle.zig (guarded by its "should expose the reference constants" test).

🤖 Generated with Claude Code

[GrapeBaBa]

Checked with my codex, these two edge cases seems not works correct.

• module exports name like that

  pub const @"__proto__" = enum(u8) {
      inherited = 7,
  };

• property name like that

  pub const SpecialTags = enum(u8) {
      @"__proto__" = 1,
      normal = 2,
  };

[nazarhussain]

Checked with my codex, these two edge cases seems not works correct.

• module exports name like that

  pub const @"__proto__" = enum(u8) {
      inherited = 7,
  };

• property name like that

  pub const SpecialTags = enum(u8) {
      @"__proto__" = 1,
      normal = 2,
  };

@GrapeBaBa These seems very narrow edge cases, can we open an issue for it and proceed with this PR as it is?

[spiral-ladder]

+1 that it's a very narrow edge case, can only be encountered according to the consumer's usage patterns, in which case i dont think we do?

[GrapeBaBa]

nit: which Nico found in my PR before, the arrow which AI used is a bit wired, suggest to use some alternatives which could input using keyboard

[GrapeBaBa]

Looks good