feat(datetime-api): add ChronoFieldDemo to showcase field-based access to LocalDateTime

What
- Introduced ChronoFieldDemo class under DateandTimeAPI package.
- Demonstrates retrieving specific temporal fields from LocalDateTime using ChronoField.
- Fields shown in example:
  - DAY_OF_MONTH → numeric day in current month.
  - AMPM_OF_DAY → 0 for AM, 1 for PM.
  - YEAR_OF_ERA → year within current era (e.g., 2025).
  - YEAR → absolute year (can be negative for BCE).

Why
- Provides a hands-on example of the java.time.temporal.ChronoField API.
- Helps learners understand how ChronoField can extract granular components of a temporal object.
- Reinforces that ChronoField values are integer-based representations useful for low-level date/time manipulation.

How to use
- Run ChronoFieldDemo main().
- The output prints current system date-time values, field by field.

Real-life applications
- Logging or auditing where only specific date parts (e.g., day, year, or AM/PM) are required.
- Custom calendar and scheduling software where calculations depend on fields rather than complete objects.
- Financial apps generating reports by month/day/year without needing entire LocalDateTime objects.
- Internationalization systems where AM/PM or era-specific year (e.g., BCE/CE) matters.

Notes
- Unlike direct getters (dt.getDayOfMonth()), ChronoField provides a uniform field-based access mechanism.
- Using ChronoField with get() throws UnsupportedTemporalTypeException if the field is not supported by
  the temporal type.
- Consider ChronoUnit for measuring differences, while ChronoField is for extraction.

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

Author: Someshdiwan

Section26DateandTimeAPI/src/DateandTimeAPI/ChronoFieldDemo.java

@@ -10,5 +10,6 @@ public static void main(String[] args) {
         System.out.println(dt.get(ChronoField.DAY_OF_MONTH));
         System.out.println(dt.get(ChronoField.AMPM_OF_DAY));
         System.out.println(dt.get(ChronoField.YEAR_OF_ERA));
+        System.out.println(dt.get(ChronoField.YEAR));
     }
 }