docs: fix cross-links after the refresh; remove the stale benchmark script

- docs/README.md links the improvement logs and June plans where the
  refresh archived them (docs/archive/).
- clawhdf5-py README: 'r+' creates and replaces attributes (compact or
  dense); only deleting them is unsupported.
- scripts/run-benchmarks.sh benchmarked the pre-rename rustyhdf5-format
  and overwrote BENCHMARKS.md; nothing referenced it. Removed.
- Cargo.toml descriptions no longer name rustyhdf5/edgehdf5; clawhdf5-gpu
  says it is not HDF5 I/O.
- benchmarks/cross_platform.sh pointed at a ROADMAP section that no longer
  exists.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

benchmarks/cross_platform.sh

@@ -29,7 +29,8 @@
 #     - Use wasm-pack with a custom bench harness
 #     - Replace std::time::Instant with web_sys::Performance::now()
 #     - Replace TempDir/HDF5 I/O with an in-memory backend (separate effort)
-#   See ROADMAP.md §WASM for the full scope.
+#   Browser reads are tested (not benchmarked) by
+#   examples/wasm-viewer/test/run.sh; see examples/wasm-viewer/README.md.
 
 set -euo pipefail