Fix OSError race condition in file polling between fileExists and getLastModificationTime

[Copilot]

Race condition in file polling: fileExists() can return true, but file gets deleted before getLastModificationTime() executes, raising unhandled OSError.

Changes

Wrapped getLastModificationTime() calls in try-except blocks at race-prone locations in src/fsnotify/filepoll.nim:

• initFileEventData: Catches OSError during file initialization, silently skips initialization if file vanishes
• filecb modification check: Catches OSError when checking existing file for changes, defers to next poll cycle
• filecb rename detection: Catches OSError when checking renamed files, marks file as non-existent and continues search
• filecb recreation: Catches OSError when reinitializing previously-removed files that reappear

# Before
if fileExists(data.name):
  let now = getLastModificationTime(data.name)  # Can raise OSError
  
# After  
if fileExists(data.name):
  try:
    let now = getLastModificationTime(data.name)
  except OSError:
    discard  # File vanished, handled on next poll

Affects Windows and macOS file monitoring (both use polling). Linux unaffected (uses inotify).

Original prompt

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This section details on the original issue you should resolve

<issue_title>getLastModificationTime can fail and raise OSError</issue_title>
<issue_description>Very rarely when polling for a file, os.getLastModificationTime can fail to find the file (as it was just removed) after os.fileExists returns true and thus raises OSError.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes getLastModificationTime can fail and raise OSError #4

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