Feature: Tax Regimes are added so that different bills with different series can be printed for Different regimes such as VAT and GST

Chore: Model relationships updated to make them simpler
Chore: Bill printing majorly refactored for it

Due to the sheer depth of the changes. There can be showstoppers. Please test it carefully

bookie/src/app/sales/reason/reason.component.ts

@@ -1,5 +1,5 @@
 import { Component, ElementRef, Inject, ViewChild } from '@angular/core';
-import { UntypedFormBuilder, UntypedFormGroup } from '@angular/forms';
+import { FormControl, FormGroup } from '@angular/forms';
 import { MAT_DIALOG_DATA, MatDialogRef } from '@angular/material/dialog';
 
 import { ReasonDatasource } from './reason-datasource';
@@ -11,7 +11,10 @@ import { ReasonDatasource } from './reason-datasource';
 })
 export class ReasonComponent {
   @ViewChild('son', { static: true }) son?: ElementRef;
-  form: UntypedFormGroup;
+  form: FormGroup<{
+    son: FormControl<string>;
+  }>;
+
   dataSource: ReasonDatasource;
   title: string;
   selected = '';
@@ -21,12 +24,11 @@ export class ReasonComponent {
   constructor(
     public dialogRef: MatDialogRef<ReasonComponent>,
     @Inject(MAT_DIALOG_DATA) private data: { title: string; reasons: string[] },
-    private fb: UntypedFormBuilder,
   ) {
-    this.reasons = data.reasons || [];
+    this.reasons = data.reasons ?? [];
     this.title = data.title;
-    this.form = this.fb.group({
-      son: '',
+    this.form = new FormGroup({
+      son: new FormControl<string>('', { nonNullable: true }),
     });
     this.dataSource = new ReasonDatasource(this.reasons);
   }