Windows drive letters are parsed as config section delimiters

Description

Absolute Windows config paths are currently parsed as if the drive-letter colon starts a config section. For example, C:\Users\name\config.yaml is split into file path C and section \Users\name\config.yaml.

This affects the config export helpers, ConfigSerializer.dump_dict, config-path detection, and lazy @config loading. On Windows, the existing CLI/config test set hits the same failure across YAML, JSON, TOML, section export, and lazy loading.

Reproduction

Paths such as these fail or resolve to the wrong file/section:

_serialize_configuration(config, to_yaml=rC:\tmp\config.yaml)
load_config_from_path(r@C:\tmp\config.yaml)

Expected behavior

The drive prefix should remain part of the path. An optional section should only be parsed from a colon after that prefix, so C:\tmp\config.yaml:model resolves to path C:\tmp\config.yaml and section model.

Start with the config export helpers, ConfigSerializer.dump_dict, config-path detection, and lazy @config loading described in the issue. Run the existing CLI/config tests covering YAML, JSON, TOML, section export, and lazy loading; done means a Windows drive prefix stays in the path while an optional later colon still selects the section.