fix: add back subcommands and add_typer (alias)

[percevalw]

Description

• Restore nested CLI applications with Cli.add_subcommands(). Confit CLI objects
  can temporarily still be mounted under Typer applications without making Typer
  a Confit dependency. Cli.add_typer() and Typer mounting now emit a visible
  deprecation warning and will be removed in the next major release.

Checklist

• If this PR is a bug fix, the bug is documented in the test suite.
• Changes were documented in the changelog (pending section).
• If necessary, changes were made to the documentation.

[github-actions]

Coverage Report

Name	Stmts	Miss	∆ Miss	Cover
TOTAL	1385	18	0	98.70%

Files without new missing coverage

Name	Stmts	Miss	∆ Miss	Cover
confit/utils/settings.py Was already missing at lines 10-12 return bool(loads(value)) - except Exception: - return True	11	2	0	81.82%
confit/registry.py Was already missing at line 132 if name is None and hasattr(e.model, "type_"): - name = e.model.type_.__module__ + "." + e.model.type_.__qualname__ e = ConfitValidationError( Was already missing at lines 545-550 """ - entrypoints = importlib_metadata.entry_points() ... - return entrypoints.get(self.entry_point_namespace, []) Was already missing at line 575 if catalogue.check_exists(*path): - return catalogue._get(path) elif from_entry_point: Was already missing at line 577 elif from_entry_point: - return from_entry_point if not catalogue.check_exists(*path): Was already missing at line 584 ) - return catalogue._get(path)	230	8	0	96.52%
confit/config.py Was already missing at line 150 if isinstance(obj, tuple): - return tuple(wrap_mapping(v) for v in obj) return obj Was already missing at line 156 if resolve: - return config.resolve(registry=registry) Was already missing at line 386 return local_names[parts] + ("." if path.endswith(":") else "") - except KeyError: raise KeyError(path) Was already missing at line 431 if not deep and len(loc) > 1: - return obj Was already missing at line 519 return - current[path] = val Was already missing at line 560 ): - old[key] = new_val else: Was already missing at line 598 elif isinstance(obj, tuple): - return tuple(rec(v) for v in obj) elif isinstance(obj, Reference): Was already missing at line 649 if isinstance(config_paths, Path): - config_paths = [config_paths]	323	8	0	97.52%

11 files skipped due to complete coverage.

Coverage success: total of 98.70% is above 98.61% 🎉