Clean up broker protocol enums

[wdcui]

Simplify broker protocol enums by removing redundant non_exhaustive markers, the WaitOutcome wrapper, and the ErrorCode::Unknown variant. Event waits now return ReadinessState directly, and unknown raw broker error codes decode as invalid wire tags.

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

Click for details

--- 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/v0.48.0/src/lints/constructible_struct_adds_field.ron

Failed in:
  field WaitEventResponse.readiness in /home/runner/work/litebox/litebox/litebox_broker_protocol/src/event.rs:49
  field WaitEventResponse.readiness in /home/runner/work/litebox/litebox/litebox_broker_protocol/src/event.rs:49

--- failure enum_missing: pub enum removed or renamed ---

Description:
A publicly-visible enum cannot be imported by its prior path. A `pub use` may have been removed, or the enum 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/v0.48.0/src/lints/enum_missing.ron

Failed in:
  enum litebox_broker_protocol::event::WaitOutcome, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/7dc0e734a3aa4f1677fa0c058ea3444ed8f3494b/litebox_broker_protocol/src/event.rs:18
  enum litebox_broker_protocol::WaitOutcome, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/7dc0e734a3aa4f1677fa0c058ea3444ed8f3494b/litebox_broker_protocol/src/event.rs:18

--- failure enum_variant_missing: pub enum variant removed or renamed ---

Description:
A publicly-visible enum has at least one variant that is no longer available under its prior name. It 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/v0.48.0/src/lints/enum_variant_missing.ron

Failed in:
  variant ErrorCode::Unknown, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/7dc0e734a3aa4f1677fa0c058ea3444ed8f3494b/litebox_broker_protocol/src/error.rs:35
  variant ErrorCode::Unknown, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/7dc0e734a3aa4f1677fa0c058ea3444ed8f3494b/litebox_broker_protocol/src/error.rs:35

--- failure struct_pub_field_missing: pub struct's pub field removed or renamed ---

Description:
A publicly-visible struct has at least one public field that is no longer available under its prior name. It 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/v0.48.0/src/lints/struct_pub_field_missing.ron

Failed in:
  field outcome of struct WaitEventResponse, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/7dc0e734a3aa4f1677fa0c058ea3444ed8f3494b/litebox_broker_protocol/src/event.rs:60
  field outcome of struct WaitEventResponse, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/7dc0e734a3aa4f1677fa0c058ea3444ed8f3494b/litebox_broker_protocol/src/event.rs:60