Function expand_git_config 

pub fn expand_git_config(git: &TomlGit) -> Result<Vec<ConfigDirective>, String>

Expand a [git] config section into directives.

The default style’s rules are emitted first (unconditional), then branch-specific overrides with BranchMatch conditions. This ensures last-match-wins semantics: branch overrides beat the default style.

Errors

Returns an error if a style name is unrecognized or a style TOML fails to parse.