fix: Code review fixes for multiple Python files

Fixed the following issues:

1. gitstatus.py:
   - Fixed broad IOError exception handling to catch specific OSError/FileNotFoundError
   - Fixed unused variable warning by using _ for ignored stderr

2. proxy.py:
   - Fixed os.path.expandvars usage that doesn't expand ~, changed to os.path.expanduser
   - Fixed check_output call that was incorrectly passing a file path instead of command list
   - Fixed missing space in env variable assignment for aliases

3. update_emoji.py:
   - Fixed file handle leaks by using with statements for file operations
   - Removed unnecessary .keys() call in dict iteration

4. cheatsheet.py:
   - Fixed parse() function to handle lines without '=' character
   - Fixed inefficient list comprehension using any() instead
   - Fixed shadowing of built-in 'cheatsheet' function name

5. ssh-agent.py:
   - Modernized string formatting from .format() to f-string

6. ssh-proxy.py:
   - Fixed next() call without default value that crashes when no proxy env vars set
   - Fixed missing exit code propagation from subprocess.call

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/shell-proxy/ssh-proxy.py

@@ -4,7 +4,10 @@ import subprocess
 import sys
 from urllib.parse import urlparse
 
-proxy = next(os.environ[_] for _ in ("HTTP_PROXY", "HTTPS_PROXY") if _ in os.environ)
+proxy = next((os.environ[_] for _ in ("HTTP_PROXY", "HTTPS_PROXY") if _ in os.environ), None)
+if proxy is None:
+    sys.stderr.write("Error: Neither HTTP_PROXY nor HTTPS_PROXY environment variable is set\n")
+    sys.exit(1)
 
 parsed = urlparse(proxy)
 
@@ -34,4 +37,4 @@ def make_argv():
     yield sys.argv[1] # host
     yield sys.argv[2] # port
 
-subprocess.call(make_argv())
+sys.exit(subprocess.call(make_argv()))