Builder pattern

Each facade exposes a fluent builder that composes a request by method chaining, terminated by .execute().

Example: `Code.search()`

results = (
    code.search()
        .in_code(NomCode.CC)
        .article_number("1382")
        .with_formatter()
        .execute()
)

Builders return Self to allow chaining; they take the LegifranceClient as the first argument.

Builder	Entry point	Typical methods
`CodeSearchBuilder`	`Code.search()`	`.in_code()`, `.text()`, `.article_number()`, `.at_date()`, `.with_formatter()`, `.paginate()`, `.execute()`
`CodeConsultFetcher`	`Code.fetch_code(id)`	`.include_abrogated()`, `.section()`, `.at(date)`
`ArticleFetcher`	`Code.fetch_article(id)`	`.at(date)`

Readability: the request reads like a sentence.
Progressivity: each step is optional and composable.
Typing: each method narrows the permissible parameters (e.g. in_code accepts a NomCode, not a str).
Discoverability: autocompletion guides the user towards valid methods.