clawhdf5-netcdf4: phony dimensions, skipped types and order as netCDF-C

Read a file's metadata the way netCDF-C 4.9.3 does (libhdf5/hdf5open.c),
for the whole file on first use (src/model.rs, replacing src/scope.rs):

- links in creation order when the group tracks it, else name order;
  a group's datasets before its subgroups; dimension ids file-wide;
- variables' dimensions from _Netcdf4Coordinates (file-wide ids), else
  the scales DIMENSION_LIST attaches when the first axis has one, else
  netCDF-C's phony dimensions phony_dim_<id> (create_phony_dims: shared
  by length and unlimitedness within a group, not between two axes of
  one variable, numbered subgroups first, a zero length unlimited);
- datasets of types netCDF-C cannot represent are not variables
  (references, bit fields, time, arrays, compounds/enums/VLENs over
  them), replaying netCDF-C's file-wide type list, failed types
  included;
- unlimited lengths as nc4_find_dim_len (its group and below).

NcType gains Enum, Compound, VLen, Opaque and is #[non_exhaustive];
Variable::nc_type is netCDF-C's type (1-byte strings NC_CHAR). New
clawhdf5_format::group_v2::links_in_creation_order_in.

Tests compare with netCDF-C itself (tests/netcdf_c_view.py calls the
libnetcdf netCDF4-python bundles through ctypes): new interop cases for
h5py files without dimension scales, every type class, link order; and
the gated corpus_vs_netcdf_c (CLAWHDF5_NETCDF_CORPUS): 420 of the 429
conformance-corpus files netCDF-C opens match (main: 68); the other 9
are explained in tests/corpus_known_differences.txt and known-issues.

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

crates/clawhdf5-netcdf4/tests/netcdf4_tests.rs

@@ -776,9 +776,12 @@ fn test_pure_dimensions_hidden_and_non_coord_names() {
         .with_shape(&[2]);
     let file = NetCDF4File::from_bytes(b.finish().unwrap()).unwrap();
 
+    // `x`, and the phony dimension netCDF-C gives the 3 values of
+    // `_nc4_non_coord_x` (no dimension scale attached).
     let dims = file.dimensions().unwrap();
-    assert_eq!(dims.len(), 1);
-    assert_eq!(dims[0].name, "x");
+    let names: Vec<&str> = dims.iter().map(|d| d.name.as_str()).collect();
+    assert_eq!(names, ["x", "phony_dim_1"]);
+    assert_eq!(dims[1].size, 3);
     let mut names = file.variable_names().unwrap();
     names.sort();
     assert_eq!(names, ["v", "x"]);
@@ -786,7 +789,8 @@ fn test_pure_dimensions_hidden_and_non_coord_names() {
     assert_eq!(x.name(), "x");
     assert_eq!(x.read_raw_f64().unwrap(), [1.0, 2.0, 3.0]);
     assert!(!x.is_coordinate());
-    // No DIMENSION_LIST: `v` gets `x` by size, as before.
+    // No DIMENSION_LIST: `v` gets the group's first dimension of its length
+    // (netCDF-C's phony rule, which also takes real dimensions).
     assert_eq!(file.variable("v").unwrap().dimensions()[0].name, "x");
 }