perf(data): compact immutable snapshots with current execution rules

crates/fidc-core/src/engine.rs

@@ -5425,7 +5425,7 @@ mod tests {
     fn market(date: NaiveDate, open: f64, close: f64) -> DailyMarketSnapshot {
         DailyMarketSnapshot {
             date,
-            symbol: SYMBOL.to_string(),
+            symbol: SYMBOL.into(),
             timestamp: Some(format!("{date} 15:00:00")),
             day_open: open,
             open,
@@ -5479,21 +5479,21 @@ mod tests {
     fn factor(date: NaiveDate) -> DailyFactorSnapshot {
         DailyFactorSnapshot {
             date,
-            symbol: SYMBOL.to_string(),
+            symbol: SYMBOL.into(),
             market_cap_bn: 10.0,
             free_float_cap_bn: 8.0,
             pe_ttm: 12.0,
             turnover_ratio: Some(1.0),
             effective_turnover_ratio: Some(1.0),
             adjustment_factor_backward1: None,
-            extra_factors: BTreeMap::new(),
+            extra_factors: Default::default(),
         }
     }
 
     fn candidate(date: NaiveDate) -> CandidateEligibility {
         CandidateEligibility {
             date,
-            symbol: SYMBOL.to_string(),
+            symbol: SYMBOL.into(),
             is_st: false,
             is_star_st: false,
             is_new_listing: false,