build(clean): ignore and remove generated MySQL parser artifacts

Context:
- Bison/Flex-generated parser files in `lib/` can be created locally during parser work.
- These files are generated artifacts and should not be tracked.

Changes:
- Add generated parser artifacts to `.gitignore`:
  - `lib/MySQL_Lexer.yy.c`
  - `lib/MySQL_Parser.output`
  - `lib/MySQL_Parser.tab.c`
  - `lib/MySQL_Parser.tab.h`
- Extend `lib/Makefile` `clean` target to remove the same generated files.

Why:
- Prevent accidental inclusion of regenerated parser outputs in feature commits.
- Keep worktrees clean and make `make clean` deterministic for parser-related changes.

.gitignore

@@ -177,6 +177,12 @@ test/tap/tests/test_cluster_sync_config/test_cluster_sync.cnf
 .aider*
 GEMINI.md
 
+# generated MySQL parser artifacts
+lib/MySQL_Lexer.yy.c
+lib/MySQL_Parser.output
+lib/MySQL_Parser.tab.c
+lib/MySQL_Parser.tab.h
+
 # Database discovery output files
 discovery_*.md
 database_discovery_report.md

lib/Makefile

@@ -121,7 +121,8 @@ $(ODIR):
 
 
 clean:
-	rm -rf *.pid $(ODIR)/*.oo $(ODIR)/*.o $(ODIR)/*.gcno $(ODIR)/*.gcda *.ko *.so *~ core libproxysql.a $(ODIR)
+	rm -rf *.pid $(ODIR)/*.oo $(ODIR)/*.o $(ODIR)/*.gcno $(ODIR)/*.gcda *.ko *.so *~ core libproxysql.a $(ODIR) \
+		MySQL_Lexer.yy.c MySQL_Parser.output MySQL_Parser.tab.c MySQL_Parser.tab.h
 
 
 ## self note