Merge branch 'fix/p1-attrs-links' into fix/p1-read-gaps

# Conflicts:
#	crates/clawhdf5-format/src/attribute.rs
#	crates/clawhdf5-format/src/group_v1.rs
#	crates/clawhdf5/src/lazy.rs
#	crates/clawhdf5/src/mmap_file.rs
#	docs/known-issues.md

docs/known-issues.md

@@ -95,12 +95,16 @@ the VDS item, which is marked.
 - **Old-style shared messages (version 1)** read the wrong address.
   **Fixed 2026-09-25:** the address follows the length-sized link-name
   offset of the embedded symbol table entry (`tcompound.h5`, `tcompound2.h5`).
-- **Array members of version-1 compound datatypes** (found while fixing the
-  items above) were read as one element — wrong data. **Fixed 2026-09-25.**
 - **Groups and links:**
   - Groups with a user-defined link type (e.g. 187) cannot be listed.
+    **Fixed 2026-09-25:** user-defined links are skipped; the rest of the
+    group lists.
   - Dense groups with more than about 22 000 links cannot be listed.
-  - Soft links are left out of `datasets()`.
+    **Fixed 2026-09-25:** two bugs — fractal-heap child indirect blocks had
+    the wrong row count, and v2 B-tree internal nodes at depth 3+ were read
+    with the wrong pointer widths.
+  - Soft links are left out of `datasets()`. **Fixed 2026-09-25:** soft
+    links are listed as their targets; dangling ones are left out.
   - **Wrong data (found while fixing user blocks):** an old-style group whose
     local-heap free list points outside the heap listed garbage names where
     libhdf5 refuses the heap. **Fixed 2026-09-25**
@@ -108,7 +112,10 @@ the VDS item, which is marked.
     libhdf5 does).
 - **Dense attributes:** a large attribute stored as a fractal-heap "huge"
   object makes every attribute on the object fail. This affects real NetCDF
-  files (`issue671.nc`).
+  files (`issue671.nc`). **Fixed 2026-09-25:** huge and tiny heap objects,
+  and filtered heaps, are read; and an attribute that still cannot be read
+  is left out of `attrs()` (reported by `attrs_with_errors()`) instead of
+  failing the others.
 - **Other readers:**
   - VL-string datasets are not readable through `File`.
   - Metadata cache images are not supported.