xml.dom.pulldom.DOMEventStream leaks file handles opened by parse()

pulldom.parse() opens a file when called with a filename string, but the resulting DOMEventStream never closes it. The class has no close() method, no context manager support, and clear() just sets self.stream = None without closing.

This produces ResourceWarning: unclosed file and can lead to file descriptor exhaustion in long-running processes.

The documentation example at https://docs.python.org/3/library/xml.dom.pulldom.html#module-xml.dom.pulldom shows:

doc = pulldom.parse('sales_items.xml')
for event, node in doc:
    ...

— with no cleanup, so users following the docs will hit this.

Reproduction

import warnings, tempfile, os, gc
from xml.dom import pulldom

warnings.simplefilter('always', ResourceWarning)

fd, path = tempfile.mkstemp(suffix='.xml')
os.write(fd, b'<root><item>test</item></root>')
os.close(fd)

events = pulldom.parse(path)
for event, node in events:
    pass

# stream is still open after full iteration
print(f'stream.closed: {events.stream.closed}')  # False

# clear() doesn't close it either
events.clear()

del events
gc.collect()  # ResourceWarning: unclosed file ...

os.unlink(path)

The existing test in test_pulldom.py already works around this with self.addCleanup(handler.stream.close) (line 36), which further confirms the leak.

Suggested fix

Track whether parse() opened the file (vs. receiving a user-provided stream), then add close(), __enter__/__exit__, and __del__ with ResourceWarning to DOMEventStream. Update clear() to close owned streams.

This follows the same approach used for ElementTree.iterparse() (gh-140601).

Linked PRs

• gh-148437

先从 DOMEventStream 和 pulldom.parse() 开始，然后检查 test_pulldom.py，尤其是第 36 行附近现有的清理。重现 ResourceWarning，并验证 filename 和用户提供的流的所有权行为。完成的标准是：通过测试覆盖生命周期清理和上下文管理器行为，且不泄漏句柄。