ENH: Add bulk getValues/setValues API to AbstractDataStore

[joeykleingers]

Summary

• Adds getValues(startIndex, span) and setValues(startIndex, span) virtual methods to AbstractDataStore<T> for bulk read/write of contiguous element ranges
• DataStore<T> overrides use std::memcpy for maximum in-memory throughput
• Rewrites fill(), copy(), copyFrom(), setTuple(), and fillTuple() to use the bulk API internally so all existing callers benefit automatically

Companion PR: https://github.com/BlueQuartzSoftware/FileStore/pull/4

Motivation

Per-element OOC access through ZarrStore::operator[] costs ~50-100ns each even when the chunk is cached (virtual dispatch -> mutex -> N-D position calc -> 6-slot FIFO cache search -> element access -> mutex unlock). Filter-level optimizations have minimized the number of accesses, but the per-access cost is fixed by the storage layer.

The bulk API allows ZarrStore (in the FileStore plugin) to override with chunk-aware implementations that use memcpy per chunk-row instead of per element, with three optimization levels:

1. Per-row memcpy — one memcpy per contiguous chunk-row (~50x reduction for 50^3 chunks)
2. Chunk-sticky — holds chunk shared_ptr across rows, avoids redundant cache lookups (~2500x fewer lookups per chunk)
3. Multi-row extension — merges rows when chunks cover full fast dimensions (up to entire chunk in one memcpy)

Implementation Details

• Default getValues/setValues on AbstractDataStore loop over getValue/setValue for backward compatibility with any subclass that doesn't override
• Uses std::make_unique<T[]> for intermediate buffers to avoid the std::vector<bool> bit-packing issue

Test Plan

• DataStore Bulk getValues/setValues — full array, partial range, boundary, roundtrip, empty span, out-of-range, single element (7 sections)
• DataStore Bulk fill / copy / copyFrom / setTuple / fillTuple
• DataStore Cross-API Roundtrip — setValue->getValues, setValues->getValue, partial writes
• DataStore Bulk getValues with multi-component — multi-dim tuples + float32
• All pre-existing DataStore/DataArray tests pass
• Both in-core and OOC builds pass (19/19 DataStore tests on each)

[JDuffeyBQ]

Changes look good. One thing is that it looks a bit odd at first to see a getValues() call with no return value. Maybe we could change the function names to make that a bit more obvious. Something like getValuesIntoBuffer(). Not a major issue but I think most of our other functions named with "get" return something so it would help differentiate them.

[imikejackson]

Changes look good. One thing is that it looks a bit odd at first to see a getValues() call with no return value. Maybe we could change the function names to make that a bit more obvious. Something like getValuesIntoBuffer(). Not a major issue but I think most of our other functions named with "get" return something so it would help differentiate them.

@joeykleingers @JDuffeyBQ
How about 'copyInto()' or 'fillBuffer()'

[imikejackson]

copyIntoBuffer
copyFromBuffer