chore: Tier 4d — hoist tempfile/criterion/half/serde to workspace.dependencies

Add [workspace.dependencies] to the root Cargo.toml for the four
duplicated-across-many-crates dependencies flagged by the earlier review:
tempfile (7 crates), criterion (6), half (4 — real version skew, clawhdf5-gpu
pinned 2.7 while others used bare 2), and serde (4). Update every consuming
crate to `dep = { workspace = true }`, preserving crate-local `optional =
true` where it already existed. half now resolves uniformly to 2.7.x
workspace-wide instead of two separate semver ranges.

Also fixed clawhdf5-filters/Cargo.toml's stale "rustyhdf5" description
while touching the file (same class of leftover rename as prior fixes).

Not touching rayon/byteorder/clap (no skew found, lower priority).

crates/clawhdf5-netcdf4/Cargo.toml

@@ -14,4 +14,4 @@ clawhdf5 = { path = "../clawhdf5", version = "2.1.0" }
 clawhdf5-format = { path = "../clawhdf5-format", version = "2.1.0" }
 
 [dev-dependencies]
-tempfile = "3"
+tempfile = { workspace = true }