chore: prepare 0.2.2 release

[adamcavendish]

Summary

Prepare the 0.2.2 release containing pointer-sized generated Rust
ApiCallError values.

Problem

The boxed error representation is merged, but the workspace version, changelog,
and stable installer documentation still identify 0.2.1.

Behavior

Surface	0.2.2 behavior
Workspace packages	Report version 0.2.2
Changelog	Publishes the boxed ApiCallError change under 0.2.2
Stable installer links	Download release 0.2.2
Rust error documentation	States the one-allocation erasure tradeoff

Compatibility

Generated Rust public error methods and calling semantics remain unchanged.
Derived Debug output reflects the private boxed inner representation, as
documented in the changelog.

Documentation

• docs/src/rust_config.md: documents that converting a typed operation error
  into pointer-sized ApiCallError performs one heap allocation while typed
  errors remain inline.

Validation

• cargo metadata --format-version=1 --locked --no-deps
• just fmt-check
• just clippy
• just book
• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!