refactor(query): extract shared Strata.SqlTools.Query model project

Moves the byte-identical 19-file ExpressionFactory/Query tree (duplicated
across Snowflake and SqlServer) into the new Strata.SqlTools.Query project
under the flat namespace Strata.SqlTools.Query. Both dialect projects now
reference the shared project; the Snowflake copies are deleted.

Also folds in the IDE0028 fix on CalculationFilterGroup.GetValidFilters
(collection expression []), which resolves both new-code IDE0028 smells
in one place now that there is a single copy.

Eliminates the 63 new duplicate lines flagged on the PR and removes the
largest contributor to the project's 11.1% duplication density. No
behavioral change: the moved types are identical to the originals.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Strata.SqlTools.Query/LogicalOperator.cs

@@ -0,0 +1,30 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Strata.SqlTools.Query;
+
+public enum LogicalOperator
+{
+    [Display(Name = "and")]
+    And,
+    [Display(Name = "or")]
+    Or
+}
+
+public static class LogicalOperatorExtensions
+{
+    public static string ToSql(this LogicalOperator logicalOperator, bool withSpaces = true)
+    {
+        var sql = "";
+        switch (logicalOperator)
+        {
+            case LogicalOperator.And:
+                sql = "and";
+                break;
+            case LogicalOperator.Or:
+                sql = "or";
+                break;
+        }
+
+        return withSpaces ? $" {sql} " : sql;
+    }
+}