feat(codec): implement Candid schema parser and codegen renderer

[b3hr4d]

This PR implements Slices 2 & 3 of the Candid Codec API:

1. Slice 3 (Parser Schema):

   • Exposes directly from Rust WASM in @ic-reactor/parser.
   • Traverses the Candid compiler's AST recursively to output a structured JSON schema.
   • Automatically appends TS type definitions after parser compilation.
   • Adds vitest suite for parser-schema validation.

2. Slice 2 (Codegen Renderer):

   • Implements in @ic-reactor/codegen.
   • Performs topological sorting of declarations to resolve dependency order.
   • Gracefully resolves cyclic references without infinite recursion.
   • Generates fully compliant @ic-reactor/cod schema builders and types.

3. Playground Integration:

   • Refactors the web playground example to use the official parseDid and generateCodecDeclarations APIs.
   • Cleans up the deprecated regex parser module.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve explicit numeric Candid field IDs

When a DID uses explicit numeric labels in a non-tuple record/variant (e.g. record { 0 : nat; name : text }), this converts Label::Id(0) to the schema name "0". The renderer then emits a normal property "0": ...; @icp-sdk/core hashes that string label instead of treating it as field id 0 (numeric IDs are represented as _0_ in the JS IDL), so the generated codec is wire-incompatible for those records/variants. Preserve the label kind or encode numeric labels in the form the IDL builder expects.

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[chatgpt-codex-connector]

Represent multi-value returns as separate returns

For methods with more than one return value, this emits a single c.tuple(...) return codec. CandidServiceCodec.toIDL() always wraps returnCodec.toIDL() in a one-element returns array, so a DID like m : () -> (nat, text) becomes [IDL.Tuple(IDL.Nat, IDL.Text)] instead of [IDL.Nat, IDL.Text]; actors generated from this codec will have the wrong Candid signature for real multi-return methods.

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[chatgpt-codex-connector]

Handle recursive type references lazily

When a schema contains a recursive type (for example type Node = record { next : opt Node }), breaking the DFS cycle here still lets rendering emit export const Node = c.record({ next: c.opt(Node) }). That reference is evaluated while Node is in its temporal dead zone, so importing the generated module throws before any codec can be used; cycles need a lazy/recursive codec representation or should be rejected instead of sorted eagerly.

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