Downsampling don't work with wildcards in key expression

[sashacmc]

Describe the bug

Seems that the method weight_at from the KeyExprTree works only with key expression without wildcards, it should be replaced with something other.

zenoh/zenoh/src/net/routing/interceptor/downsampling.rs

Line 125 in 2500e5a

if let Some(id) = ke_id.weight_at(&key_expr.clone()) {

To reproduce

Run z_pub in router mode
Run z_sub in client mode with config

      "downsampling": [
          {
              "flow": "ingress",
              "rules": [
                  {
                      "freq": 0.1,
                      "key_expr": "demo/**"
                  }
              ]
          },
      ],

Downsampling not work.

When replacing demo/** with demo/example/zenoh-rs-pub everything works as expected

System info

Any platform