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]>

crates/clawhdf5-io/Cargo.toml

@@ -3,7 +3,7 @@ name = "clawhdf5-io"
 version = "2.7.0"
 edition = "2024"
 rust-version.workspace = true
-description = "I/O abstraction layer for rustyhdf5"
+description = "I/O adapters for clawhdf5 (buffers, mmap, prefetch)"
 license = "MIT"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"
 readme = "README.md"