Limit nested filters to avoid stack overflow 2

[manunio]

This will fix: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=66029.
This pr includes all the work at #979 done by @djc as well as updated ui test.

For ui test: I think previous input for filter-recursion ui test was not right as it
was not triggering error for recursion itself, for example:

#[test]
fn fuzzed_filter_recursion() {
    const TEMPLATE: &str = include_str!("../tests/filter-recursion.txt");
    if let Err(e) = Ast::from_str(TEMPLATE, None, &Syntax::default()) {
        panic!("{e}");
    }
}

---- tests::fuzzed_filter_recursion stdout ----
thread 'tests::fuzzed_filter_recursion' panicked at askama_parser/src/tests.rs:952:9:
failed to parse template source at row 1, column 255 near:
"|A|AA|A|A|A|A|AA|A|A|A|A|AA|A|A|A|A|AA|A"...

[GuillaumeGomez]

Looks good to me, thanks!

[djc]

Level is Copy, why break the convention of passing it by value here?

[manunio]

It was copied from your old pr: #979