feat: update math cell to display user selected base units

Still need to force recalculation when default base units are changed. Also, will need to update plot cells which will required updates to the Python code to include user base units (requires update to PlotData type).

src/MathCell.svelte

@@ -6,7 +6,7 @@
   import { isFiniteImagResult, type Result, type FiniteImagResult,
            type PlotResult, type MatrixResult, isMatrixResult } from "./resultTypes";
            import type { CodeFunctionQueryStatement, QueryStatement } from "./parser/types";
-  import { convertUnits, unitsValid } from "./utility";
+  import { convertUnits } from "./utility";
   import type { MathCellConfig } from "./sheet/Sheet";
   import type MathCell from "./cells/MathCell";
   import PlotCell from "./cells/PlotCell";
@@ -133,13 +133,20 @@
       };
     }
 
-    if ( statement.units ) {
-      // unit conversion required to user supplied units
-      resultUnitsLatex = statement.unitsLatex;
-      resultUnits = statement.units;
+    if ( statement.units || result.customUnitsDefined) {
+      // unit conversion required to user supplied units or sheet level user default units
+      // user supplied units in the statement takes precedence over sheet level user default units 
+
+      if (statement.units) {
+        resultUnitsLatex = statement.unitsLatex;
+        resultUnits = statement.units;
+      } else {
+        resultUnitsLatex = result.customUnitsLatex;
+        resultUnits = result.customUnits;
+      } 
 
       if (result.numeric && result.real && result.finite && !numberConfig.symbolicOutput) {
-        const {newValue: localNewValue, unitsMismatch: localUnitsMismatch} = convertUnits(result.value, result.units, statement.units);
+        const {newValue: localNewValue, unitsMismatch: localUnitsMismatch} = convertUnits(result.value, result.units, resultUnits);
 
         if (!localUnitsMismatch) {
           resultLatex = customFormat(localNewValue, numberConfig.formatOptions);
@@ -152,9 +159,9 @@
       } else if (isFiniteImagResult(result) && !numberConfig.symbolicOutput) {
         // handle unit conversion for imaginary number
         const {newValue: newRealValue, unitsMismatch: realUnitsMismatch} = 
-                convertUnits(result.realPart, result.units, statement.units);
+                convertUnits(result.realPart, result.units, resultUnits);
         const {newValue: newImagValue, unitsMismatch: imagUnitsMismatch} = 
-                convertUnits(result.imagPart, result.units, statement.units);
+                convertUnits(result.imagPart, result.units, resultUnits);
 
         if (!realUnitsMismatch && !imagUnitsMismatch) {
           resultLatex = formatImag(newRealValue, newImagValue, numberConfig);