ci: wire up CI, fix no_std build, fix stale package names in scripts

- Add .gitea/workflows/ci.yml running scripts/ci-test.sh (fmt, clippy,
  test, no_std check) on push/PR to main.
- Fix stale rustyhdf5-py/rustyhdf5-format package names in
  ci-test.sh/check-nostd.sh, which had been silently no-op'ing those
  checks (cargo warns but doesn't fail on an unknown --exclude/-p
  target).
- With those checks actually running, fix the real issues they surface:
  - clippy: useless_conversion in chunked_write.rs, byte_char_slices in
    global_heap.rs/object_header.rs.
  - cargo fmt: apply formatting across the workspace (whitespace only).
  - no_std (thumbv7em-none-eabihf) build errors in clawhdf5-format:
    core::sync::atomic::AtomicU64 doesn't exist on that target (no
    native 64-bit atomics) — switch profiling.rs's counters to
    portable-atomic, which falls back to a CAS-based emulation there
    and is a no-op wrapper elsewhere. Add missing alloc imports for
    Box (filters.rs), Vec (filters_szip.rs), and format! (dict_encoding.rs)
    on no_std paths. Replace f64::powi (std/libm-only) with a small
    local exponentiation-by-squaring helper in the scale-offset filter.

crates/clawhdf5-bench/benches/h5bench_read.rs

@@ -74,11 +74,7 @@ fn bench_read_sequential(c: &mut Criterion) {
             let data: Vec<f32> = (0..nn).map(|i| i as f32 * 0.001).collect();
             {
                 let lf = hdf5::File::create(&path).unwrap();
-                let lds = lf
-                    .new_dataset::<f32>()
-                    .shape([nn])
-                    .create("data")
-                    .unwrap();
+                let lds = lf.new_dataset::<f32>().shape([nn]).create("data").unwrap();
                 lds.write(data.as_slice()).unwrap();
             }
             b.iter(|| {
@@ -235,19 +231,23 @@ fn bench_read_zerocopy_mmap(c: &mut Criterion) {
 
         group.throughput(Throughput::Bytes((n * size_of::<f64>()) as u64));
 
-        group.bench_with_input(BenchmarkId::new("clawhdf5_mmap_zerocopy", n), &path, |b, p| {
-            b.iter(|| {
-                let file = MmapFile::open(p).unwrap();
-                let ds = file.dataset("data").unwrap();
-                let slice = ds.read_f64_zerocopy().unwrap();
-                // Sum every element to force the mapped pages to actually be
-                // faulted in — returning just `.len()` would measure nothing
-                // but the mmap() syscall, repeating the exact "too-fast-to-
-                // be-real" mistake this benchmark exists to fix.
-                let sum: f64 = slice.map(|s| s.iter().sum()).unwrap_or(0.0);
-                criterion::black_box(sum)
-            });
-        });
+        group.bench_with_input(
+            BenchmarkId::new("clawhdf5_mmap_zerocopy", n),
+            &path,
+            |b, p| {
+                b.iter(|| {
+                    let file = MmapFile::open(p).unwrap();
+                    let ds = file.dataset("data").unwrap();
+                    let slice = ds.read_f64_zerocopy().unwrap();
+                    // Sum every element to force the mapped pages to actually be
+                    // faulted in — returning just `.len()` would measure nothing
+                    // but the mmap() syscall, repeating the exact "too-fast-to-
+                    // be-real" mistake this benchmark exists to fix.
+                    let sum: f64 = slice.map(|s| s.iter().sum()).unwrap_or(0.0);
+                    criterion::black_box(sum)
+                });
+            },
+        );
 
         group.bench_with_input(BenchmarkId::new("clawhdf5_copy", n), &path, |b, p| {
             b.iter(|| {