h5rs: URLs as FILE arguments (feature remote)

With the `remote` feature (`remote-https` for https://), ls, dump, stat
and diff take an http(s):// (or s3://, gs://, az:// with those
clawhdf5-remote features) URL wherever they take a file, and read it by
range requests through clawhdf5-remote's block cache. check validates
every byte, so it downloads a remote file whole and checks it as before.
Without the feature a URL is a clean error naming it.

The tools read the file through File::storage instead of as_bytes: object
headers, shared messages, attributes, v1 and v2 group links, dense
storage (fractal heaps and v2 B-trees), path resolution, chunk listings
and variable-length values go through the format crate's *_in functions,
and the fractal-heap block verifier reads each block through the storage
(a read failure of a remote file is reported as a problem, not as "past
the end of the file"). A local file's storage is its mapped bytes, so its
reads are still slices. stat's file size comes from the opened file, so
it is right for a URL.

Tests: tests/remote.rs serves fixtures (old and new formats, a paged
file, a metadata cache image, a multi-block fractal heap, compounds, v1
groups) with the clawhdf5-remote test server and requires every
subcommand's output and exit status for the URL to equal the local
file's, and diff of the two to be clean; 404s, non-HDF5 bodies and
https without its feature are clean errors. Local output is unchanged:
the old and new h5rs print the same for ls -r -v, dump, stat and check
--data on the 747 conformance and CVE corpus files (tank, 2026-09-26;
the dumps of h5diff_hyper1/2.h5 were too large for the comparison
script, their ls, stat and check agree), except cve-2025-2310.h5, whose
dump error messages differ between runs of the old binary too (which
failing chunk is reported first).

ci-test.sh lints h5rs with remote-https, runs the URL tests and checks
h5rs with remote for C.

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

crates/clawhdf5-tools/src/diff.rs

@@ -174,7 +174,7 @@ pub fn run(args: &mut Args, out: &mut Out) -> std::io::Result<i32> {
     }
     let mut files = Vec::new();
     for f in &pos[..2] {
-        match H5::open(std::path::Path::new(f)) {
+        match H5::open_arg(f) {
             Ok(mut h) => {
                 if let Some(m) = max_bytes {
                     h.max_bytes = m;