fix: treat EOF on stdin as 'quit' in --interactive prompt

[Eljees]

Fixes #1897.

isort --interactive loops on input() inside ask_whether_to_apply_changes_to_file, so when standard input is closed or has no more data — stdin redirected from an empty source, or a terminal wrapper that doesn't provide a readable stdin, as in the Git-Bash report — input() raises EOFError and isort prints an "unrecoverable exception" traceback. The reproduction is not Windows-specific: the same happens on Linux with isort --interactive < /dev/null.

Since no answer can ever arrive once stdin is exhausted, the prompt now treats EOF the same way as an explicit quit: exit cleanly with a short explanatory message instead of a traceback.

The regression test patches builtins.input to raise EOFError and asserts a clean SystemExit; it fails on main (the EOFError propagates) and passes with the fix. The rest of tests/unit/test_format.py is unchanged and green.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.37%. Comparing base (131f4ad) to head (8721a1b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2653   +/-   ##
=======================================
  Coverage   99.37%   99.37%           
=======================================
  Files          41       41           
  Lines        3181     3184    +3     
  Branches      686      686           
=======================================
+ Hits         3161     3164    +3     
  Misses         12       12           
  Partials        8        8           

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