fix(api): use .round() on sat_per_vbyte_to_feerate

Only casting to `u64` would always round down.
Rounding (`.round()`) and then casting to `u64`
is more precise.

Also updates the fee JSON on `test_feerate_parsing`
with current values which include sub-1 sat fees:

```
curl https://mempool.space/api/fee-estimates | jq 'to_entries | sort_by(.key | tonumber) | from_entries'
```

Author: luisschwab

src/api.rs

@@ -490,7 +490,7 @@ pub struct MempoolFeesSubmitPackage {
 pub(crate) fn sat_per_vbyte_to_feerate(estimates: HashMap<u16, f64>) -> HashMap<u16, FeeRate> {
     estimates
         .into_iter()
-        .map(|(k, v)| (k, FeeRate::from_sat_per_kwu((v * 250_000.0) as u64)))
+        .map(|(k, v)| (k, FeeRate::from_sat_per_kwu((v * 250_000.0).round() as u64)))
         .collect()
 }
 

src/lib.rs

@@ -510,36 +510,35 @@ mod test {
     fn test_feerate_parsing() {
         let esplora_fees_raw = serde_json::from_str::<HashMap<u16, f64>>(
             r#"{
-  "25": 1.015,
-  "5": 2.3280000000000003,
-  "12": 2.0109999999999997,
-  "15": 1.018,
-  "17": 1.018,
-  "11": 2.0109999999999997,
-  "3": 3.01,
-  "2": 4.9830000000000005,
-  "6": 2.2359999999999998,
-  "21": 1.018,
-  "13": 1.081,
-  "7": 2.2359999999999998,
-  "8": 2.2359999999999998,
-  "16": 1.018,
-  "20": 1.018,
-  "22": 1.017,
-  "23": 1.017,
-  "504": 1,
-  "9": 2.2359999999999998,
-  "14": 1.018,
-  "10": 2.0109999999999997,
-  "24": 1.017,
-  "1008": 1,
-  "1": 4.9830000000000005,
-  "4": 2.3280000000000003,
-  "19": 1.018,
-  "144": 1,
-  "18": 1.018
-}
-"#,
+    "1": 1.952,
+    "2": 1.952,
+    "3": 1.199,
+    "4": 1.013,
+    "5": 1.013,
+    "6": 1.013,
+    "7": 1.013,
+    "8": 1.013,
+    "9": 1.013,
+    "10": 1.013,
+    "11": 1.013,
+    "12": 1.013,
+    "13": 0.748,
+    "14": 0.748,
+    "15": 0.748,
+    "16": 0.748,
+    "17": 0.748,
+    "18": 0.748,
+    "19": 0.748,
+    "20": 0.748,
+    "21": 0.748,
+    "22": 0.748,
+    "23": 0.748,
+    "24": 0.748,
+    "25": 0.748,
+    "144": 0.693,
+    "504": 0.693,
+    "1008": 0.693
+}"#,
         )
         .unwrap();
 
@@ -550,16 +549,21 @@ mod test {
         assert!(convert_fee_rate(1, HashMap::new()).is_none());
         assert_eq!(
             convert_fee_rate(6, esplora_fees.clone()),
-            Some(FeeRate::from_sat_per_kwu((2.236_f64 * 250_000.0) as u64))
+            Some(FeeRate::from_sat_per_kwu(
+                (1.013_f64 * 250_000.0).round() as u64
+            )),
+            "should inherit from value for target=6"
         );
         assert_eq!(
             convert_fee_rate(26, esplora_fees.clone()),
-            Some(FeeRate::from_sat_per_kwu((1.015_f64 * 250_000.0) as u64)),
-            "should inherit from value for 25"
+            Some(FeeRate::from_sat_per_kwu(
+                (0.748_f64 * 250_000.0).round() as u64
+            )),
+            "should inherit from value for target=25"
         );
         assert!(
             convert_fee_rate(0, esplora_fees).is_none(),
-            "should not return feerate for 0 target"
+            "should not return feerate for target=0"
         );
     }