v0.14.1

Changed

• Boxed the internal AppError payload inside a new ErrorInner allocation,
  keeping public field access via Deref while shrinking the error to a
  pointer-sized handle that shares metadata, retry hints, and backtrace state.

Removed

• Dropped clippy::result_large_err allowances in response helpers and tests
  now that AppError is pointer-sized and lint-clean without suppressions.

Fixed

• Removed the unused BacktraceSlot::get helper to restore builds with -D warnings.
• Simplified the metrics recorder test harness with dedicated types to satisfy
  clippy::type_complexity without sacrificing coverage.