feat: Add canister-metadata-section function

[adamspofford-dfinity]

This PR adds a function to the sync plugin interface to fetch metadata sections from canisters. This is useful for type-checking canister calls by fetching candid:service. (Does this function need to be so specific instead of fetching state-tree content? Yes, because plugins should be usable from a canister host, and canisters cannot fetch the state tree, but rather get metadata sections by calling a management canister method only available to canisters.)

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[Copilot]

Pull request overview

Adds canister metadata-section reads to sync plugins, supporting direct and proxy-routed access.

Changes:

• Extends the WIT interface and runtime host implementation.
• Updates examples, schemas, and documentation.
• Adds undeclared-target and integration coverage.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
examples/icp-sync-plugin/README.md	Documents metadata reads.
examples/icp-sync-plugin/plugin/src/lib.rs	Demonstrates the new host function.
examples/icp-sync-plugin/icp.yaml	Publishes example Candid metadata.
docs/schemas/icp-yaml-schema.json	Updates plugin permissions description.
docs/schemas/canister-yaml-schema.json	Updates plugin permissions description.
docs/reference/configuration.md	Documents metadata access configuration.
docs/guides/writing-sync-plugins.md	Adds authoring guidance and example.
docs/concepts/sync-plugins.md	Defines routing and return semantics.
crates/icp/src/manifest/adapter/plugin.rs	Updates manifest field documentation.
crates/icp-sync-plugin/tests/fixtures/test-plugin/src/lib.rs	Adds an undeclared-target fixture.
crates/icp-sync-plugin/sync-plugin.wit	Adds the metadata request and import.
crates/icp-sync-plugin/src/runtime.rs	Implements direct and proxied metadata reads.
crates/icp-sync-plugin/DESIGN.md	Records implementation rationale.
crates/icp-sync-plugin/Cargo.toml	Adds management-canister types.
crates/icp-cli/tests/sync_tests.rs	Tests absent metadata through both routes.
Cargo.lock	Records the dependency update.

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[raymondk]

can't this reuse icp::operations::misc::fetch_canister_metadata ?

[raymondk]

or: https://github.com/dfinity/icp-cli/blob/main/crates/icp/src/operations/wasm.rs#L12 ?

[raymondk]

.... it would introduce a cycle....