chore: release v0.4.0

[github-actions]

🤖 New release

• rmcp-macros: 0.3.2 -> 0.4.0
• rmcp: 0.3.2 -> 0.4.0 (⚠ API breaking changes)

⚠ rmcp breaking changes

--- failure constructible_struct_adds_field: externally-constructible struct adds field ---

Description:
A pub struct constructible with a struct literal has a new pub field. Existing struct literals must be updated to include the new field.
        ref: https://doc.rust-lang.org/reference/expressions/struct-expr.html
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.41.0/src/lints/constructible_struct_adds_field.ron

Failed in:
  field Tool.output_schema in /tmp/.tmpyzb7O3/rust-sdk/crates/rmcp/src/model/tool.rs:25
  field CallToolResult.structured_content in /tmp/.tmpyzb7O3/rust-sdk/crates/rmcp/src/model.rs:1195

--- failure struct_missing: pub struct removed or renamed ---

Description:
A publicly-visible struct cannot be imported by its prior path. A `pub use` may have been removed, or the struct itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.41.0/src/lints/struct_missing.ron

Failed in:
  struct rmcp::model::PromptTemplate, previously in file /tmp/.tmptt2CJ1/rmcp/src/model/prompt.rs:158
  struct rmcp::model::PromptArgumentTemplate, previously in file /tmp/.tmptt2CJ1/rmcp/src/model/prompt.rs:166

--- failure trait_no_longer_dyn_compatible: trait no longer dyn compatible ---

Description:
Trait is no longer dyn compatible, which breaks `dyn Trait` usage.
        ref: https://doc.rust-lang.org/stable/reference/items/traits.html#object-safety
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.41.0/src/lints/trait_no_longer_dyn_compatible.ron

Failed in:
  trait IntoCallToolResult in file /tmp/.tmpyzb7O3/rust-sdk/crates/rmcp/src/handler/server/tool.rs:184

Changelog

rmcp-macros

0.4.0 - 2025-08-05

Added

• [breaking] Add support for Tool.outputSchema and CallToolResult.structuredContent (#316)

Other

• README.md codeblock terminator (#348)

rmcp

0.4.0 - 2025-08-05

Added

• [breaking] Add support for Tool.outputSchema and CallToolResult.structuredContent (#316)

Fixed

• don't wrap errors in streamable http auth client (#353)
• (prompt) remove unused code (#343)

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This PR was generated with release-plz.