fix: close file descriptor in LocalEnvironment._update_cwd

[vominh1919]

Problem

LocalEnvironment._update_cwd() uses a bare open(self._cwd_file).read() call that never closes the file descriptor. This method runs on every terminal command execution, so the fd leaks accumulate over time in long sessions.

Fix

Use a with statement so the fd is released promptly.

# Before
cwd_path = open(self._cwd_file).read().strip()

# After
with open(self._cwd_file) as f:
    cwd_path = f.read().strip()

Impact

Prevents file descriptor exhaustion in long-running sessions with many terminal commands.

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Standalone resubmission of the fd-leak fix from #15552 (1 file, 2 lines changed).

[vominh1919]

@teknium1 please check Sir

[alt-glitch]

Likely duplicate of #8112 — same fd leak fix in LocalEnvironment._update_cwd(). Also a resubmission of closed #15552.

[vominh1919]

Likely duplicate of #8112 — same fd leak fix in LocalEnvironment._update_cwd(). Also a resubmission of closed #15552.

I resubmission of #15552