clawhdf5-remote: block cache and HTTP range reads (open_url)

Range-read milestone M3, first half: a new crate with the block cache the
design makes mandatory for remote files and an HTTP backend, so
open_url("http://...") gives a clawhdf5::File over File::open_storage.

BlockCache wraps any Storage: aligned blocks (1 MiB by default, the size
docs/design/range-reads.md section 2 measured), LRU with a byte budget,
the missing blocks of one read_at/read_ranges fetched with one backend
read_ranges call as runs of consecutive blocks (a one-block gap filled to
merge runs, each request at most 8 MiB), and reads that miss more than
half the budget not kept. Thread-safe without holding the lock across a
fetch: a block being fetched is in flight, a second reader waits for it
instead of fetching it again, and a failed fetch fails its waiters and is
not cached. A backend holding the file in memory passes through.

HttpStorage (ureq, no TLS by default; `https` adds rustls with ring):
opening is one ranged GET of the first block, whose Content-Range gives
the length (the cache keeps the bytes). The file is pinned by a strong
ETag (If-Match), else Last-Modified (If-Unmodified-Since), and its length,
checked on every response: a change is RemoteError::FileChanged, never
mixed data. A server that ignores Range is refused without reading the
body unless a full download is allowed. Connection errors, timeouts,
408/429/5xx and short bodies are retried with exponential backoff;
Accept-Encoding: identity, and an encoded body is refused. read_ranges
fetches its ranges in parallel.

Tests (a std-only HTTP/1.1 server in tests/common/server.rs, also the
range_server example): every fixture read over HTTP gives File::open's
transcript (CLAWHDF5_REMOTE_CORPUS adds the conformance corpus), with
request counts per file with and without the cache; an h5py-written file
against libhdf5's values; a multi-block file fetched in whole blocks, each
once; a server ignoring Range; a file replaced mid-read (ETag,
Last-Modified, length only); truncated bodies and 503s (retried, then an
error, never cached); a slow server with 8 concurrent readers (no block
fetched twice); bad URLs, 404, encoded bodies, non-HDF5 data. The cache
has unit tests for coalescing, splitting, LRU order, large reads,
failures and concurrent in-flight dedup.

ci-test.sh: clawhdf5-remote joins the no-C default-build check, and its
https feature is linted.

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

scripts/ci-test.sh

@@ -109,23 +109,36 @@ run_step "cargo clippy (fast-deflate / zlib-ng)" cargo clippy \
     --features clawhdf5-format/fast-deflate,clawhdf5-filters/fast-deflate \
     -- -D warnings
 
+# clawhdf5-remote's HTTPS backend (rustls).
+run_step "cargo clippy (remote, https)" cargo clippy \
+    -p clawhdf5-remote \
+    --all-targets \
+    --features https \
+    -- -D warnings
+
 # The README promises that the core crates build no C by default. Hold it to
 # that: fail if a crate that compiles C (a *-sys crate, cc or cmake) enters the
 # default dependency tree of any of them. clawhdf5-migrate (bundled SQLite),
 # clawhdf5-napi (Node) and clawhdf5-gpu (graphics drivers) are exempt.
 # js-sys (clawhdf5-wasm's bindings to JavaScript) builds no C.
+# clawhdf5-remote is checked by default (plain HTTP); its https feature
+# (ring) builds C and is opt-in.
 no_c_in_default_build() {
-    local crate found=0
-    for crate in clawhdf5-format clawhdf5-io clawhdf5-filters clawhdf5 \
+    local entry crate features found=0
+    for entry in clawhdf5-format clawhdf5-io clawhdf5-filters clawhdf5 \
         clawhdf5-agent clawhdf5-ann clawhdf5-accel clawhdf5-netcdf4 clawhdf5-cli \
         clawhdf5-tools \
-        clawhdf5-wasm; do
+        clawhdf5-wasm \
+        clawhdf5-remote; do
+        crate=${entry%%:*}
+        features=()
+        [ "$entry" != "$crate" ] && features=(--features "${entry#*:}")
         local c_deps
-        c_deps=$(cargo tree -q -p "$crate" -e normal,build --prefix none \
+        c_deps=$(cargo tree -q -p "$crate" "${features[@]}" -e normal,build --prefix none \
             | grep -E '^([a-z0-9_-]+-sys|cc|cmake) v' \
             | grep -v '^js-sys v' | sort -u)
         if [ -n "$c_deps" ]; then
-            echo "$crate pulls in C by default:"
+            echo "$entry pulls in C by default:"
             echo "$c_deps" | sed 's/^/    /'
             found=1
         fi