Split Resampler into capability traits Adjustable and Resizable

[HEnquist]

Builds on the next4.0 branch. Moves the capability-specific methods off the single Resampler trait into dedicated traits, turning two runtime errors into compile-time capabilities while keeping Resampler as the universal trait for mixed Box<dyn Resampler> collections.

Changes

• New Adjustable<T>: Resampler<T> — set_resample_ratio, set_resample_ratio_relative
• New Resizable<T>: Resampler<T> — set_chunk_size
• Resampler::as_adjustable() / as_resizable() recover the capability from a trait object (default None; Async returns Some(self), Fft does not)
• Removed the now-unreachable ResampleError::SyncNotAdjustable and ChunkSizeNotAdjustable variants

[Copilot]

Pull request overview

Refactors the resampler API to model “can adjust resample ratio” and “can resize chunk size” as compile-time capabilities via dedicated traits, while keeping Resampler as the common trait for Box<dyn Resampler<_>> use cases.

Changes:

• Split capability-specific methods into new traits: Adjustable<T> (ratio adjustment) and Resizable<T> (chunk size adjustment).
• Added Resampler::as_adjustable() / as_resizable() to recover capabilities from &mut dyn Resampler<T> (default None; Async returns Some(self)).
• Removed the now-unreachable runtime error variants (SyncNotAdjustable, ChunkSizeNotAdjustable) and updated docs/examples/tests accordingly.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/lib.rs	Introduces Adjustable/Resizable traits, adds capability query methods on Resampler, and adds tests validating trait-object capability recovery.
src/asynchro.rs	Implements the new capability traits for Async and wires as_adjustable()/as_resizable() to return Some(self).
src/synchro.rs	Removes now-obsolete “not adjustable” ratio setters from the synchronous Fft resampler implementation.
src/error.rs	Removes obsolete error variants and updates documentation links to reference the new capability traits.
README.md	Documents the API change and shows updated usage patterns for concrete types vs dyn Resampler.
examples/polyfixedin_ramp64.rs	Updates imports to bring Adjustable into scope for ratio ramping calls.
examples/fixedout_ramp64.rs	Updates imports to bring Adjustable into scope for ratio ramping calls.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.