Function implementation 

pub fn implementation(
    qualifiers: Vec<GeneratedToken>,
    parameters: Vec<Vec<GeneratedToken>>,
    trait_path: Option<Vec<GeneratedToken>>,
    target: Vec<GeneratedToken>,
    predicates: Vec<Vec<GeneratedToken>>,
    items: Vec<GeneratedToken>,
) -> Result<Vec<GeneratedToken>, Overflow>

One inherent or trait implementation with exact qualifiers, parameters, target, predicates and items.

An absent trait path emits an inherent implementation. Qualifiers are emitted exactly before impl, so an unsafe implementation remains explicit caller authority.

Errors

Returns Overflow where the implementation body outgrows the declared generated-token magnitude.