Optimize lookup functions by caching array accesses (#296)

Reduced redundant array accesses in tableValue, lookupTable, and
lookupArray functions. Each iteration now caches the lookup result
in a local variable instead of accessing the same array element
twice (once for keyHash and once for key).

This reduces array subscript overhead in hot paths during table
and key lookups, particularly beneficial for documents with many
nested tables.

Author: dduan

Sources/TOMLDecoder/Parsing/Parser.swift

@@ -1840,19 +1840,22 @@ extension Parser {
     func tableValue(tableIndex: Int, keyed: Bool, key: String, keyHash: Int) -> InternalTOMLTable.Value? {
         let table = keyed ? keyTables[tableIndex].table : tables[tableIndex]
         for kv in table.keyValues {
-            if keyValues[kv].keyHash == keyHash, keyValues[kv].key == key {
+            let kvPair = keyValues[kv]
+            if kvPair.keyHash == keyHash, kvPair.key == key {
                 return .keyValue(kv)
             }
         }
 
         for arr in table.arrays {
-            if keyArrays[arr].keyHash == keyHash, keyArrays[arr].key == key {
+            let arrPair = keyArrays[arr]
+            if arrPair.keyHash == keyHash, arrPair.key == key {
                 return .array(arr)
             }
         }
 
         for table in table.tables {
-            if keyTables[table].keyHash == keyHash, keyTables[table].key == key {
+            let tablePair = keyTables[table]
+            if tablePair.keyHash == keyHash, tablePair.key == key {
                 return .table(table)
             }
         }
@@ -1864,7 +1867,8 @@ extension Parser {
         let table = keyed ? keyTables[tableIndex].table : tables[tableIndex]
         for i in 0 ..< table.tables.count {
             let tableIndexAtPosition = table.tables[i]
-            if keyTables[tableIndexAtPosition].keyHash == keyHash, keyTables[tableIndexAtPosition].key == key {
+            let tablePair = keyTables[tableIndexAtPosition]
+            if tablePair.keyHash == keyHash, tablePair.key == key {
                 return tableIndexAtPosition
             }
         }
@@ -1875,7 +1879,8 @@ extension Parser {
         let table = keyed ? keyTables[tableIndex].table : tables[tableIndex]
         for i in 0 ..< table.arrays.count {
             let arrayIndex = table.arrays[i]
-            if keyArrays[arrayIndex].keyHash == keyHash, keyArrays[arrayIndex].key == key {
+            let arrPair = keyArrays[arrayIndex]
+            if arrPair.keyHash == keyHash, arrPair.key == key {
                 return arrayIndex
             }
         }