Allow passing `filters: Vec<Filter>` directly to `BgpkitParser`

[JustinLoye]

Thank you for your work on bgpkit-parser.
I am building on top of it bgpflux, a clone of bgpreader, and the experience is great!

I have however a minor ergonomic request about the filters and how they are bound to BgpkitParser.

Filter is already a public, well-designed type, but the only way to attach filters to a BgpkitParser is through add_filter(&str, &str). This means a parser's filter construction is always mediated through a parser instance: it's not possible to build a filter specification once in a Vec<Filter> independently and reuse it across multiple parsers, which is unfortunate because BgpkitParser already stores filters as Vec<Filter> internally.

Could you consider adding a method that accepts a pre-built Vec<Filter> directly, bypassing string re-parsing?
Something like:

impl<R> BgpkitParser<R> {
    pub fn with_filters(self, filters: Vec<Filter>) -> Self {
        BgpkitParser {
            filters,
            ..self
        }
    }
}

[digizeph]

Great idea! Will add this and bundle it with the next release