mypy(config[snapshot]): Add override for property/field conflicts

why:
- Snapshot classes have properties that conflict with dataclass field names during type checking
- These property/field collisions cause mypy to generate false positive error messages
- We need to silence these specific errors without compromising overall type safety

what:
- Added [[tool.mypy.overrides]] section in pyproject.toml for libtmux.snapshot module
- Set disable_error_code = ["override"] to silence property override errors
- Placed the override in a module-specific section to limit scope and prevent disabling
  this error check for other modules

refs: Complements the snapshot class refactoring to ensure clean mypy checks

Author: tony

pyproject.toml

@@ -141,6 +141,10 @@ disable_error_code = ["method-assign"]
 module = "libtmux._internal.frozen_dataclass_sealable"
 disable_error_code = ["method-assign"]
 
+[[tool.mypy.overrides]]
+module = "libtmux.snapshot"
+disable_error_code = ["override"]
+
 [[tool.mypy.overrides]]
 module = "tests._internal.test_frozen_dataclass_sealable"
 ignore_errors = true