feat: add stable ValueKind inspection

[tiye]

Summary

• add RFC 0093 for stable host-side value type tags
• expose ValueKind and Value::kind() plus Value::is_nil()
• extend external embedding tests and five-language manuals

Validation

• make check
• strict make api-doc via the check target
• make docs

Hosts can branch on value types without inspecting internal Rc/container representations; runtime and bytecode semantics are unchanged.

[Copilot]

Pull request overview

This PR introduces a stable, host-facing type-tag API (ValueKind, Value::kind(), and Value::is_nil()) so embedders can branch on QuickCoffee value types without relying on internal Rc/container representations, while keeping runtime and bytecode semantics unchanged.

Changes:

• Add ValueKind plus Value::kind() / Value::is_nil() to the public embedding surface and re-export them from the crate root.
• Extend the embedding API tests to use the new type-tag inspection.
• Document the new inspection APIs via RFC 0093 and propagate the embedding guidance across manuals and generated docs.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/embedding_api.rs	Adds assertions for Value::kind() / Value::is_nil() in the public embedding tests.
src/vm.rs	Defines ValueKind and implements Value::kind() / Value::is_nil() on Value.
src/lib.rs	Re-exports ValueKind from the crate root for embedders.
RFCs/0093-value-kind-inspection.md	Introduces and records the stable value-kind inspection contract (RFC 0093).
README.md	Updates the RFC range to include RFC 0093.
manuals/manual.zh-CN.qc	Mentions Value::kind() / Value::is_nil() in the embedding notes.
manuals/manual.latin.qc	Mentions Value::kind() / Value::is_nil() in the embedding notes.
manuals/manual.en.qc	Mentions Value::kind() / Value::is_nil() in the embedding notes.
manuals/manual.devanagari-sa.qc	Mentions Value::kind() / Value::is_nil() in the embedding notes.
manuals/manual.classical-zh.qc	Mentions Value::kind() / Value::is_nil() in the embedding notes.
docs/manual.zh-CN.md	Updates generated manual content to reference stable type checks.
docs/manual.zh-CN.html	Updates generated manual content to reference stable type checks.
docs/manual.latin.md	Updates generated manual content to reference stable type checks.
docs/manual.latin.html	Updates generated manual content to reference stable type checks.
docs/manual.en.md	Updates generated manual content to reference stable type checks.
docs/manual.en.html	Updates generated manual content to reference stable type checks.
docs/manual.devanagari.sa.md	Updates generated manual content to reference stable type checks.
docs/manual.devanagari-sa.html	Updates generated manual content to reference stable type checks.
docs/manual.classical-zh.md	Updates generated manual content to reference stable type checks.
docs/manual.classical-zh.html	Updates generated manual content to reference stable type checks.

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