Flip BINARY_VERSION URLs to unified after mirror consolidation

[waltsims]

Goal

Once the 5 mirror binary repos are consolidated into waltsims/kspacefirstorder-unified (tracked at waltsims/kspacefirstorder-unified#13), flatten URL_DICT in kwave/__init__.py to point at unified release URLs instead of 5 separate mirror URLs.

Today

# 5 separate per-platform mirror URLs:
URL_BASE + "kspaceFirstOrder-CUDA-linux/releases/download/{VERSION}/..."
URL_BASE + "kspaceFirstOrder-CUDA-windows/releases/download/{VERSION}/..."
URL_BASE + "kspaceFirstOrder-OMP-linux/releases/download/{VERSION}/..."
URL_BASE + "kspaceFirstOrder-OMP-windows/releases/download/{VERSION}/..."
URL_BASE + "k-wave-omp-darwin/releases/download/{VERSION}/..."

Goal

# Single unified release with platform-named assets:
URL_BASE + "kspacefirstorder-unified/releases/download/{VERSION}/kspaceFirstOrder-CUDA-linux"
# etc.

Why

• One URL pin to maintain per release (not 5)
• Provenance: one release tag → one set of binaries, all built from the same SHA
• Drops get_windows_release_urls() indirection
• Eliminates the per-platform version drift that v0.6.2 already had to clean up (CUDA-linux at v1.3.1, others at v1.3.0, darwin at v0.3.0rc3)

Blocked by

waltsims/kspacefirstorder-unified#13 — until unified actually hosts releases with the per-platform assets, k-wave-python has nowhere to point.

Timing

Slot for k-wave-python v0.6.3 or whatever release follows the upstream consolidation. Captured in plans/release-strategy.md.

[waltsims]

Reopening — this is the consumer-side partner for waltsims/kspacefirstorder-unified#13. Was closed prematurely during v0.6.2 cleanup; the URL flip is still pending unified consolidation, which is now starting on branch consolidate-mirror-repos.

Once unified ships its first consolidated binary release, this issue lands in the same k-wave-python release as the URL flip (likely v0.6.3 or v0.7.0).