db: refactor to only init mongo client & collections once

Streetwriters.Data/UnitOfWork.cs

@@ -23,24 +23,16 @@ using Streetwriters.Data.Interfaces;
 
 namespace Streetwriters.Data
 {
-    public class UnitOfWork : IUnitOfWork
+    public class UnitOfWork(IDbContext dbContext) : IUnitOfWork
     {
-        private readonly IDbContext dbContext;
-
-        public UnitOfWork(IDbContext _dbContext)
-        {
-            dbContext = _dbContext;
-        }
-
         public async Task<bool> Commit()
         {
-            var changeAmount = await dbContext.SaveChanges();
-            return changeAmount > 0;
+            return await dbContext.SaveChanges() > 0;
         }
 
         public void Dispose()
         {
-            this.dbContext.Dispose();
+            dbContext.Dispose();
         }
     }
 }