fix: resolve CI linting and code quality issues

- Remove unused imports across all generator files
- Remove unused variables (spec, url_params, query_params, test_name)
- Fix f-strings without placeholders in auth.py and go.py
- Fix duplicate BASIC auth handling with wrong indentation
- Add missing pytest fixtures (sample_openapi_spec, temp_spec_file, temp_json_spec_file)
- Add missing TemplateRenderError import to generator files

api_testgen/cli/main.py

@@ -1,10 +1,6 @@
 """CLI interface for API TestGen."""
 
-from pathlib import Path
-from typing import Optional
-
 import click
-import yaml
 
 from ..core import SpecParser, AuthConfig
 from ..core.exceptions import InvalidOpenAPISpecError, UnsupportedVersionError
@@ -57,7 +53,7 @@ def parse_spec(ctx: click.Context):
 
     try:
         parser = SpecParser(spec_path)
-        spec = parser.load()
+        parser.load()
 
         info = parser.get_info()
         endpoints = parser.get_endpoints()