Close the TSV file when building the UMLS semantic-type tree

[Chessing234]

Bug

construct_umls_tree_from_tsv in
scispacy/umls_semantic_type_tree.py leaks the TSV file handle on
every call: it iterates the file via

for line in open(cached_path(filepath), "r"):
    ...

and never closes the returned file object. CPython will eventually
close it when reference counting drops to zero, but that's non-trivial
to guarantee in practice (e.g. long-running processes that build the
tree repeatedly, or runtimes without reference counting such as PyPy),
so each call can leave one file descriptor open until a GC cycle runs.

Root cause

The loop stores the open file only in the implicit iterator of the
for, so there's no handle to close. There's also no with
block to tie the lifetime of the file to the parsing.

Why the fix is correct

• Other scispacy modules (file_cache.py, linking_utils.py, etc.)
  all open files via with open(...) as f:; the new code matches
  that convention.
• Behaviour is preserved exactly: same file, same iteration order, same
  parsing logic inside the loop; only the lifetime management changes.
• No call sites need to be updated – the function signature and
  return value are unchanged.

Change

scispacy/umls_semantic_type_tree.py: wrap the TSV iteration in
with open(cached_path(filepath), "r") as tsv_file: and iterate
tsv_file. Small indentation change inside the for block; no
other logic touched.