[ui5-calendar]: excessive DateFormat instance creation causes memory and performance issues

### Bug Description

## Description

The `ui5-calendar` component (and its sub-components `DayPicker`, `YearPicker`, `YearRangePicker`) creates a large number of `DateFormat`
instances on every render cycle without caching or reusing them. This leads to high memory consumption and noticeable page lag when
multiple calendar instances are present on the same page.

A single Calendar render cycle can create **8–15+ fresh `DateFormat` instances** depending on which picker is visible and whether a
secondary calendar type is configured. With multiple calendars on the page this compounds quickly, causing visible lag when interacting
with the calendar.

https://github.com/user-attachments/assets/468d5eac-772d-4796-acbb-ec406c68080a

## Steps to Reproduce

### Observe instance creation for a single calendar

1. Edit `packages/main/test/pages/Calendar.html` to contain only one `<ui5-calendar>`:
```html
<body>
   <ui5-calendar></ui5-calendar>
</body>
```

2. In `packages/localization/src/DateFormat.ts`, add a `console.log` inside `getDateInstance()` to log each created instance:
```ts
static getDateInstance(oFormatOptionsOrLocale?: DateFormatOptions | LocaleWrapped, oLocale?: LocaleWrapped): DateFormat {
      if (oFormatOptionsOrLocale instanceof LocaleWrapped) {
         return DateFormatWrapped.getDateInstance(undefined, oFormatOptionsOrLocale);
      }
      const nativeLocale = oLocale ?? new LocaleWrapped(getLocale().toString());
      const date = DateFormatWrapped.getDateInstance(oFormatOptionsOrLocale, nativeLocale);
      console.log("DateFormat instance created", date);
      if (!window.dateformatinstances) {
         window.dateformatinstances = new Set();
      }
      window.dateformatinstances.add(date);
      return date;
}
```

3. Open the test page in the browser and open DevTools Console.

4. Interact with the calendar (navigate between months, open year/month picker) and observe how many `DateFormat instance created` log
lines appear.

5. Run the following in the console to check the total count:
```js
console.log("Total DateFormat instances:", window.dateformatinstances.size);
```

### Observe the impact with 20 calendars

6. Revert `Calendar.html` to render 20 calendars:
```html
<body>
   <ui5-calendar></ui5-calendar>
   <ui5-calendar></ui5-calendar>
   
</body>
```

7. Reload the page and observe the console — the instance count grows proportionally.

8. Interact with any calendar and notice the **lag** — each interaction triggers a new batch of `DateFormat` instances across all visible
sub-components.

## Expected Behavior

`DateFormat` instances with identical configuration (same format pattern and calendar type) should be created once and reused across
renders — consistent with the existing caching pattern in `DateComponentBase.getISOFormat()`.

### Affected Component

ui5-calendar

### Isolated Example

_No response_

### Steps to Reproduce

1.
2.
3.
...


### Log Output, Stack Trace or Screenshots

_No response_

### Priority

None

### UI5 Web Components Version

nightly

### Browser

Chrome

### Operating System

_No response_

### Additional Context

_No response_

### Organization

_No response_

### Declaration

- [x] I’m not disclosing any internal or sensitive information.

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[ui5-calendar]: excessive DateFormat instance creation causes memory and performance issues #13414

Bug Description

Description

Steps to Reproduce

Observe instance creation for a single calendar

Observe the impact with 20 calendars

Expected Behavior

Affected Component

Isolated Example

Steps to Reproduce

Log Output, Stack Trace or Screenshots

Priority

UI5 Web Components Version

Browser

Operating System

Additional Context

Organization

Declaration

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

[ui5-calendar]: excessive DateFormat instance creation causes memory and performance issues #13414

Description

Bug Description

Description

Steps to Reproduce

Observe instance creation for a single calendar

Observe the impact with 20 calendars

Expected Behavior

Affected Component

Isolated Example

Steps to Reproduce

Log Output, Stack Trace or Screenshots

Priority

UI5 Web Components Version

Browser

Operating System

Additional Context

Organization

Declaration

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions