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-accel/Cargo.toml

@@ -15,7 +15,7 @@ float16 = ["dep:half"]
 avx512 = []
 
 [dependencies]
-half = { version = "2", optional = true }
+half = { workspace = true, optional = true }
 
 [package.metadata.docs.rs]
 features = []