blank_lines_lower_bound ignores impl/traits functions

Version: rustfmt 2.0.0-rc.2-nightly (cc5521d9 2021-10-23)
rustfmt.toml:

tab_spaces = 2
blank_lines_lower_bound = 1

Before

fn a() {}
fn b() {}
mod foo {
  fn a() {}
  fn b() {}
}
struct Foo;
impl Foo {
  fn a() {}
  fn b() {}
}
trait Bar {
  fn a();
  fn b();
}

After (currently)

fn a() {}

fn b() {}

mod foo {

  fn a() {}

  fn b() {}
}

struct Foo;

impl Foo {
  fn a() {}
  fn b() {}
}

trait Bar {
  fn a();
  fn b();
}

After (what I think it should be formatted as)

fn a() {}

fn b() {}

mod foo {
  fn a() {}

  fn b() {}
}

struct Foo;

impl Foo {
  fn a() {}

  fn b() {}
}

trait Bar {
  fn a();
  
  fn b();
}

Related to #2954, also would be nice to have this https://github.com/rust-lang/rustfmt/issues/3382#issuecomment-793084299

Start by running rustfmt with the shown rustfmt.toml settings against the Before example and compare the output with the requested formatting. Trace the blank_lines_lower_bound handling for functions inside mod, impl, and trait blocks; done means those functions receive the configured separation without changing the other demonstrated formatting.