fixes #20057

Summary

This PR ensures that files opened internally by BinTableHDU.load() are always closed, even when parsing raises an exception.

Previously, the internal load helpers explicitly called fileobj.close() only at the end of the function. If parsing failed before reaching that point, the file handle remained open until it was eventually released by the interpreter, which can lead to file-locking issues on platforms such as Windows.

What changed

This PR updates the following helper methods:

• _load_data
• _load_coldefs

When these helpers receive a path-like object, they now open the file using a context manager and recursively invoke the existing parsing logic with the opened file object.

Behavior for caller-provided file objects is unchanged—the helper only manages the lifetime of files that it opens itself.

Why this approach?

These helpers support two kinds of inputs:

• path-like objects (where the helper owns the file object), and
• already-open file objects (which remain owned by the caller).

Using a context manager for path-like inputs guarantees that internally opened files are closed even if parsing raises an exception, while preserving the existing behavior for caller-owned file objects.

Regression test

A regression test has been added for BinTableHDU.load().

The test passes malformed column-definition input through the public API, verifies that the expected parsing exception is raised, and then immediately removes the temporary files. This confirms that internally opened file handles are released correctly. On Windows, this also prevents file-locking issues caused by unclosed handles.

Motivation

While investigating BinTableHDU.load(), I found that parsing exceptions could bypass the explicit cleanup path, leaving internally opened files open until they were later released by the interpreter.

This change makes resource cleanup exception-safe without changing parsing behavior, exception types, or the public API.

If there's a preferred approach for handling ownership of internally opened file objects, I can update the implementation accordingly.