Refactor search in files/iterative file processing

* Introduce abstractions: FileCollection, FileProxy
* Unify handling of pattern search in project files
  (source code vs. all files)

This prepares for processing of external files,
which can implement FileProxy differently.

test/solidlsp/python/test_python_basic.py

@@ -214,28 +214,28 @@ class TestProjectBasics:
         """Test search_files_for_pattern with various patterns and glob filters."""
         # Test 1: Search for class definitions across all files
         class_pattern = r"class\s+\w+\s*(?:\([^{]*\)|:)"
-        matches = project.search_source_files_for_pattern(class_pattern)
+        matches = project.search_project_files_for_pattern(class_pattern)
         assert len(matches) > 0
         # Should find multiple classes like User, Item, BaseModel, etc.
         assert len(matches) >= 5
 
         # Test 2: Search for specific class with include glob
         user_class_pattern = r"class\s+User\s*(?:\([^{]*\)|:)"
-        matches = project.search_source_files_for_pattern(user_class_pattern, paths_include_glob="**/models.py")
+        matches = project.search_project_files_for_pattern(user_class_pattern, paths_include_glob="**/models.py")
         assert len(matches) == 1  # Should only find User class in models.py
         assert matches[0].source_file_path is not None
         assert "models.py" in matches[0].source_file_path
 
         # Test 3: Search for method definitions with exclude glob
         method_pattern = r"def\s+\w+\s*\([^)]*\):"
-        matches = project.search_source_files_for_pattern(method_pattern, paths_exclude_glob="**/models.py")
+        matches = project.search_project_files_for_pattern(method_pattern, paths_exclude_glob="**/models.py")
         assert len(matches) > 0
         # Should find methods in services.py but not in models.py
         assert all(match.source_file_path is not None and "models.py" not in match.source_file_path for match in matches)
 
         # Test 4: Search for specific method with both include and exclude globs
         create_user_pattern = r"def\s+create_user\s*\([^)]*\)(?:\s*->[^:]+)?:"
-        matches = project.search_source_files_for_pattern(
+        matches = project.search_project_files_for_pattern(
             create_user_pattern, paths_include_glob="**/*.py", paths_exclude_glob="**/models.py"
         )
         assert len(matches) == 1  # Should only find create_user in services.py
@@ -244,7 +244,7 @@ class TestProjectBasics:
 
         # Test 5: Search for a pattern that should appear in multiple files
         init_pattern = r"def\s+__init__\s*\([^)]*\):"
-        matches = project.search_source_files_for_pattern(init_pattern)
+        matches = project.search_project_files_for_pattern(init_pattern)
         assert len(matches) > 1  # Should find __init__ in multiple classes
         # Should find __init__ in both models.py and services.py
         assert any(match.source_file_path is not None and "models.py" in match.source_file_path for match in matches)
@@ -252,7 +252,7 @@ class TestProjectBasics:
 
         # Test 6: Search with a pattern that should have no matches
         no_match_pattern = r"def\s+this_method_does_not_exist\s*\([^)]*\):"
-        matches = project.search_source_files_for_pattern(no_match_pattern)
+        matches = project.search_project_files_for_pattern(no_match_pattern)
         assert len(matches) == 0
 
     @pytest.mark.parametrize("language_server", PYTHON_BACKEND_LANGUAGES, indirect=True)