perf: pre-compute quoted column names for DataTable.Update RowUpdating handler

The RowUpdating event fires once per INSERT row during DataTable.Update().
Previously the handler iterated all columns, called commandBuilder.QuoteIdentifier
for every refreshable column, and allocated a ResizeArray on every row.

Column metadata (AutoIncrement/AllowDBNull flags) and quoted column names are
constant for the lifetime of a single Update() call, so we pre-compute them
once before subscribing:

- alwaysRefreshQuoted: quoted names for AutoIncrement columns (server always
  supplies the value)
- maybeRefreshCols: (DataColumn, quotedName) pairs for AllowDBNull columns;
  only added per-row when the row has no explicit value

This eliminates O(columns) QuoteIdentifier calls and a full column-iteration
per INSERT row, replacing them with a single pre-computation and a cheaper
per-row scan over the smaller maybeRefreshCols array.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 2 people

src/SqlClient/DataTable.fs

@@ -56,19 +56,30 @@ type DataTable<'T when 'T :> DataRow>(selectCommand: SqlCommand, ?connectionStri
             selectCommand.Connection <- new SqlConnection( connectionString.Value.Value)
 
         use dataAdapter = new SqlDataAdapter(selectCommand)
-        use commandBuilder = new SqlCommandBuilder(dataAdapter) 
+        use commandBuilder = new SqlCommandBuilder(dataAdapter)
+
+        // Pre-compute per-column metadata once rather than inside the per-row event handler.
+        // AutoIncrement columns always need a server-side refresh; AllowDBNull columns need one
+        // only when the row has no explicit value.  Quoting column names is also constant.
+        let alwaysRefreshQuoted =
+            [| for c in this.Columns do
+                if c.AutoIncrement then
+                    yield "inserted." + commandBuilder.QuoteIdentifier c.ColumnName |]
+        let maybeRefreshCols =
+            [| for c in this.Columns do
+                if c.AllowDBNull && not c.AutoIncrement then
+                    yield c, "inserted." + commandBuilder.QuoteIdentifier c.ColumnName |]
+
         use __ = dataAdapter.RowUpdating.Subscribe(fun args ->
             timeout |> Option.iter (fun x -> args.Command.CommandTimeout <- int x.TotalSeconds)
 
             if  args.Errors = null && args.StatementType = StatementType.Insert
                 && defaultArg batchSize dataAdapter.UpdateBatchSize = 1
-            then 
-                let columnsToRefresh = ResizeArray()
-                for c in this.Columns do
-                    if c.AutoIncrement  
-                        || (c.AllowDBNull && args.Row.IsNull c.Ordinal)
-                    then 
-                        columnsToRefresh.Add( "inserted." + commandBuilder.QuoteIdentifier c.ColumnName)
+            then
+                let columnsToRefresh = ResizeArray(alwaysRefreshQuoted)
+                for c, quotedName in maybeRefreshCols do
+                    if args.Row.IsNull c.Ordinal then
+                        columnsToRefresh.Add quotedName
 
                 if columnsToRefresh.Count > 0
                 then