feat: enhanced typehints and typing (#27)

Even tough some structures are refactored, no public API is changed.
No runtime is changed.
TypeCheckers might behave differently, which is intentional due to bug fixes. This is considered a non-breaking change, as it does not affect runtime. 

---------

Signed-off-by: Jan Kowalleck <jan.kowalleck@gmail.com>

.gitignore

@@ -2,6 +2,7 @@
 # Exclude coverage
 test-reports
 
+/.pytype/
 
 # Exlude IDE related files
 .idea/*

.pytype.toml

@@ -0,0 +1,89 @@
+# config file for https://pypi.org/project/pytype/
+# generated via `pytype --generate-config .pytype.toml`
+# run via `pytype --config .pytype.toml`
+
+# NOTE: All relative paths are relative to the location of this file.
+
+[tool.pytype]
+
+# Space-separated list of files or directories to exclude.
+exclude = [
+    '**/*_test.py',
+    '**/test_*.py',
+]
+
+# Space-separated list of files or directories to process.
+inputs = [
+    'serializable',
+    # 'tests/model.py'
+]
+
+# Keep going past errors to analyze as many files as possible.
+keep_going = true
+
+# Run N jobs in parallel. When 'auto' is used, this will be equivalent to the
+# number of CPUs on the host system.
+# jobs = 4
+
+# All pytype output goes here.
+output = '.pytype'
+
+# Platform (e.g., "linux", "win32") that the target code runs on.
+# platform = 'linux'
+
+# Paths to source code directories, separated by ':'.
+pythonpath = '.'
+
+# Python version (major.minor) of the target code.
+# python_version = '3.7'
+
+# Enable parameter count checks for overriding methods. This flag is temporary
+# and will be removed once this behavior is enabled by default.
+overriding_parameter_count_checks = true
+
+# Enable parameter count checks for overriding methods with renamed arguments.
+# This flag is temporary and will be removed once this behavior is enabled by
+# default.
+overriding_renamed_parameter_count_checks = false
+
+# Use the enum overlay for more precise enum checking. This flag is temporary
+# and will be removed once this behavior is enabled by default.
+use_enum_overlay = false
+
+# Variables initialized as None retain their None binding. This flag is
+# temporary and will be removed once this behavior is enabled by default.
+strict_none_binding = false
+
+# Support the third-party fiddle library. This flag is temporary and will be
+# removed once this behavior is enabled by default.
+use_fiddle_overlay = false
+
+# Opt-in: Do not allow Any as a return type.
+no_return_any = false
+
+# Experimental: Infer precise return types even for invalid function calls.
+precise_return = false
+
+# Experimental: Solve unknown types to label with structural types.
+protocols = false
+
+# Experimental: Only load submodules that are explicitly imported.
+strict_import = false
+
+# Experimental: Enable exhaustive checking of function parameter types.
+strict_parameter_checks = false
+
+# Experimental: Emit errors for comparisons between incompatible primitive
+# types.
+strict_primitive_comparisons = false
+
+# Experimental: Check that variables are defined in all possible code paths.
+strict_undefined_checks = false
+
+# Space-separated list of error names to ignore.
+disable = [
+    'pyi-error',
+]
+
+# Don't report errors.
+report_errors = true