Rust SDK: add agent reflection and dynamic invocation

[noise64]

• resolves GOL-48
• adds Rust discovery, graph-backed SchemaRef JSON packing, reflected clients, caller-owned typed contracts, and schema-free DynamicAgentClient invocation
• resolves caller-owned identity metadata by environment-unique type name while keeping caller codecs authoritative
• uses asynchronous awaited invocation for live streams and rejects unsupported streams in trigger, pending-input, and scheduled calls
• adds the common and Rust reflection skills, generated guide, and harness coverage
• stacked on Add generic agent reflection and TypeScript clients #3777

Verification

• Rust reflection library tests: 4 passed
• cargo fmt check for the Rust SDK
• clippy for golem-rust and golem-rust-macro with all targets and export_golem_agentic
• Rust reflection scenario harness dry-run
• documentation drift check
• golem-00 force-build, fresh local deployment, discovery, and live invocation proof across caller-codec, reflected JSON, reflected value, and direct value paths

[github-actions]

📖 Docs preview: https://docs-idc7zcuc7-golem-cloud.vercel.app

Built from commit 53461fd48ca11955d2700dce5677172adb42f46c by docs.yaml.