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-format/src/selection.rs

@@ -587,7 +587,7 @@ mod tests {
         // start=0 stride=1 count=1 block=4, version 3, enc_size 2, rank 1.
         let bytes = [
             0x02, 0, 0, 0, // type = HYPER
-            0x03, 0, 0, 0, // version 3
+            0x03, 0, 0, 0,    // version 3
             0x01, // flags = regular
             0x02, // enc_size = 2
             0x01, 0, 0, 0, // rank = 1