feat(datetime-api): add DateDemo showcasing legacy Date vs java.time API

What
- Introduced DateDemo under DateandTimeAPI package.
- Demonstrates usage of both legacy java.util.Date and modern java.time API.
- Key operations shown:
  - Printing current date/time using Date.
  - Modifying time via setHours() (legacy, deprecated).
  - Creating LocalDate with different factories:
    - now() with system default clock.
    - now(ZoneId) for specific time zones.
    - of(year, month, day) for explicit date.
    - ofEpochDay() using epoch days.
    - parse("yyyy-MM-dd") for ISO-8601 parsing.
  - Performing date arithmetic with plusMonths().
  - Using LocalTime and LocalDateTime to retrieve and manipulate times.
  - Accessing LocalDateTime components (nano, day of month).

Why
- Highlights contrast between mutable, deprecated java.util.Date and immutable, thread-safe java.time classes.
- Provides hands-on examples for creating, parsing, and manipulating dates and times.
- Reinforces why java.time is preferred in modern applications.

How to use
- Run DateDemo.
- Output will display:
  1. Current date/time using legacy Date.
  2. Modified Date after setHours().
  3. Current LocalDate in different ways (default, zone-based, explicit).
  4. Dates created from epoch days and parsing.
  5. LocalTime with subtraction of hours.
  6. LocalDateTime with nano precision and day-of-month extraction.

Real-life applications
- Parsing user-input dates in forms (LocalDate.parse).
- Scheduling events in specific time zones (LocalDate.now(ZoneId)).
- Handling recurring billing cycles or reminders (plusMonths()).
- Capturing precise timestamps for logging/auditing (LocalDateTime.now()).
- Migrating legacy Date-based code to modern java.time API.

Notes
- java.util.Date is mutable and has deprecated methods (`setHours()`).
- LocalDate, LocalTime, LocalDateTime are immutable and safe for concurrency.
- java.time supports time zones via ZoneId and ZonedDateTime.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section26DateandTimeAPI/src/JodaTimeAPI/DateDemo.java renamed to Section26DateandTimeAPI/Date/src/DateDemo.java

@@ -1,24 +1,25 @@
-package JodaTimeAPI;
-
 import java.time.*;
 import java.util.Date;
-import java.util.Locale;
 
 public class DateDemo {
     public static void main(String[] args) {
         Date d = new Date();
-        System.out.println("Todays Date and Time: "+d);
+
+        System.out.println("Today's Date and Time: "+d);
 
         //d.setTime(21);
         d.setHours(21);
+
         System.out.println(d);
 
-        //LocalDate dt = new LocalDate(); //you can not create a new date.
+        //LocalDate dt = new LocalDate();
+        //you can not create a new date.
 
         LocalDate dt = LocalDate.now();
         System.out.println(dt);
 
-        LocalDate d2 = LocalDate.now(Clock.systemDefaultZone()); //new date not able to create . Now means today date.
+        LocalDate d2 = LocalDate.now(Clock.systemDefaultZone());
+        //the new date is not able to create. Now means date today.
         System.out.println(d2);
 
         LocalDate d3 = LocalDate.now(ZoneId.of("Asia/Kolkata"));
@@ -50,4 +51,4 @@ public static void main(String[] args) {
         System.out.println(dt1.getNano());
         System.out.println(dt1.getDayOfMonth());
     }
-}
+}