Add hacking check to ban eventlet imports

Ironic has fully removed its usage of eventlet. This change
introduces a new hacking check to ban any new eventlet imports
from being added to the codebase.

This follows the post-migration guidance from the eventlet
removal documentation:
https://removal.eventlet.org/guide/post-migration-guidance/#hacking-checks

Generated-By: gemini-cli and gemini-2.5-pro
Change-Id: I48ac535325f68ba0b2a9f50aec4ce19ac6265e77
Signed-off-by: Hervé Beraud <hberaud@redhat.com>

ironic/hacking/checks.py

@@ -31,6 +31,10 @@ underscore_import_check = re.compile(r"(.)*import _(.)*")
 custom_underscore_check = re.compile(r"(.)*_\s*=\s*(.)*")
 
 
+# I319: eventlet import not allowed
+_eventlet_re = re.compile(r"\b(import|from)\s+eventlet\b")
+
+
 @core.flake8ext
 def check_explicit_underscore_import(logical_line, filename):
     """Check for explicit import of the _ function
@@ -52,3 +56,10 @@ def check_explicit_underscore_import(logical_line, filename):
     elif (translated_log.match(logical_line)
           or string_translation.match(logical_line)):
         yield (0, "N323: Found use of _() without explicit import of _!")
+
+
+@core.flake8ext
+def no_eventlet_imports(logical_line):
+    """Check for eventlet imports."""
+    if _eventlet_re.search(logical_line):
+        yield 0, "I319: eventlet import not allowed"

tox.ini

@@ -180,8 +180,10 @@ per-file-ignores =
 
 [flake8:local-plugins]
 # [N323] Found use of _() without explicit import of _!
+# [I319] eventlet import not allowed
 extension =
   N323 = checks:check_explicit_underscore_import
+  I319 = checks:no_eventlet_imports
 paths = ./ironic/hacking/
 
 [hacking]