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-io/Cargo.toml

@@ -15,13 +15,13 @@ memmap2 = { version = "0.9", optional = true }
 libc = { version = "0.2", optional = true }
 tokio = { version = "1", features = ["fs", "io-util"], optional = true }
 reqwest = { version = "0.12", features = ["json"], optional = true }
-serde = { version = "1", features = ["derive"], optional = true }
+serde = { workspace = true, optional = true }
 serde_json = { version = "1", optional = true }
 mpi = { version = "0.8", optional = true }
 
 [dev-dependencies]
 tokio = { version = "1", features = ["full"] }
-tempfile = "3"
+tempfile = { workspace = true }
 
 [features]
 default = []