Replace RuntimeError with custom exception hierarchy

[lesnik512]

Problem

All errors raised by the framework use the built-in RuntimeError. This forces users to either catch the very broad RuntimeError (which also matches unrelated runtime issues) or rely on string matching to distinguish failure modes.

Current call sites:

• modern_di/container.py — scope-mismatch, max-scope-reached, missing-provider, skipped-scope, circular-dependency
• modern_di/providers/factory.py — argument-resolution failures
• modern_di/registries/providers_registry.py — duplicate provider type
• modern_di/registries/cache_registry.py — finalizer cleanup errors (sync + async)
• modern_di/group.py — Group instantiation attempt

These cover several semantically distinct conditions, but downstream code can't tell them apart programmatically.

Proposed Solution

Introduce a small exception hierarchy in modern_di/errors.py (or a new modern_di/exceptions.py), all rooted at a base ModernDIError(RuntimeError) so existing user code that catches RuntimeError keeps working.

A first-pass mapping that aligns with the existing error templates:

ModernDIError(RuntimeError)
├── ContainerError
│   ├── ScopeMismatchError       # CONTAINER_SCOPE_IS_LOWER_ERROR, CONTAINER_NOT_INITIALIZED_SCOPE_ERROR
│   ├── ScopeSkippedError        # CONTAINER_SCOPE_IS_SKIPPED_ERROR
│   └── MaxScopeReachedError     # CONTAINER_MAX_SCOPE_REACHED_ERROR
├── ResolutionError
│   ├── ProviderNotRegisteredError   # CONTAINER_MISSING_PROVIDER_ERROR
│   ├── ArgumentResolutionError      # FACTORY_ARGUMENT_RESOLUTION_ERROR
│   └── CircularDependencyError      # CYCLE_DEPENDENCY_ERROR
├── RegistrationError
│   └── DuplicateProviderTypeError   # PROVIDER_DUPLICATE_TYPE_ERROR
├── FinalizerError                   # cache_registry sync/async cleanup
└── GroupInstantiationError          # group.py

Each exception type would carry the structured fields it currently formats into a string (e.g. ArgumentResolutionError(arg_name, arg_type, bound_type)), making programmatic introspection possible.

Impact

• Users can write narrow except CircularDependencyError: / except ProviderNotRegisteredError: blocks instead of matching on RuntimeError message strings.
• Tests in this repo currently rely on pytest.raises(RuntimeError, match=...) — they can migrate to typed assertions, which are stricter and don't break when wording is improved.
• Inheriting from RuntimeError preserves backwards compatibility for anyone catching the broad type today.
• Pairs well with Include dependency path in resolution error messages #170 (dependency-path context) since structured exceptions are a natural place to attach the resolution chain.

Complexity

Low–medium. Mechanical change: define classes, swap raise RuntimeError(...) sites, update tests. No behavior change beyond exception type.