Add a format

A format is a unit struct implementing dspk_io::core::Format, listed in the registry.

pub trait Format: Send + Sync {
    /// Stable name ("raw", "zarr-traces", "nwb", ...).
    fn name(&self) -> &'static str;
    /// Whether `path` is in this format, from its path and metadata only.
    fn detect(&self, path: &Path) -> bool;
    /// The signals `path` offers, from metadata only.
    fn sources(&self, path: &Path) -> DspResult<Vec<SourceEntry>>;
    /// Opens source `id`.
    fn open(&self, path: &Path, id: &str) -> DspResult<Box<dyn RecordingSource>>;
}

detect and sources must never read sample data: they run on every file a user points at.

The reader

open returns a dspk_core::RecordingSource:

• info() describes the recording.
• read(channels, samples, out) fills out, channel-major, scaled to each channel’s unit.
• read_stored(channels, samples, out) fills out with the stored values, before gain and offset.

Implement read_stored whenever the file holds integers. It’s what lets pipelines move compact samples and convert them on the device.

Where it goes

Kind	Crate
A generic format	dspk-io, listed in its registry
A neural format	dspk-synapse’s io, listed in its formats()

Order matters in the registry: formats are tried in order, so a more specific format goes first.

Test

Round-trip through a small file on disk, check detect refuses other formats, and compare read_stored with read through the gain and offset.