PHP 8.x: Undefined array key warnings in dynamic-value-provider.php when ACF field key lacks colon separator

### Description

Elementor Pro's ACF dynamic tag integration floods PHP error logs with Undefined array key 0 and Undefined array key 1 warnings on every page request that renders an ACF dynamic tag. The warnings originate from dynamic-value-provider.php line 16 where array destructuring is performed on the result of explode(':', $key) without any null-safety guard.
The issue was introduced by a PHP 8.x behavioral change - PHP 7.x silently returned null for undefined array keys, while PHP 8.x emits E_WARNING. The warnings fire on every ACF dynamic tag render across multiple tag types (acf-text.php, acf-url.php, and others that call the same method).
In our production environment running 4 EC2 instances behind an AWS Application Load Balancer, the warning volume was significant enough to:

Flood PHP-FPM error logs and nginx error logs (via catch_workers_output)
Contribute to PHP-FPM worker pool exhaustion (pm.max_children hit at 40 workers)
Cause client-facing 460 errors (ALB client disconnects due to slow PHP-FPM response)

All ACF fields referenced in Elementor's stored post meta were verified as properly registered and fully supported per Elementor's own documentation. The issue is not a field configuration problem - it is a PHP 8.x compatibility regression in Elementor Pro's code.

File: elementor-pro/modules/dynamic-tags/acf/dynamic-value-provider.php
Line 16:
php[ $field_key, $meta_key ] = explode( ':', $key );

When $key does not contain a : separator, explode() returns a single-element array. Destructuring into two variables then produces Undefined array key 0 and Undefined array key 1 warnings under PHP 8.x.

### Steps to reproduce

Install WordPress with PHP 8.x
Install Elementor Pro and Advanced Custom Fields (ACF)
Create an ACF field group with any supported field type (URL, Text, Email)
Create a page using Elementor Pro and add an ACF dynamic tag referencing any registered field
Visit the page
Check PHP error log — Undefined array key 0 and Undefined array key 1 warnings will appear for every page load

### Expected behavior

No PHP warnings should be emitted during normal ACF dynamic tag rendering. The code should safely handle cases where the key format does not produce the expected two-part array after explode().

Replace line 16 in dynamic-value-provider.php:
php// Current code — no null-safety guard
[ $field_key, $meta_key ] = explode( ':', $key );

Suggested fix:
Replace line 16 in dynamic-value-provider.php:

// Fixed code — null guards
$parts = explode( ':', $key );
$field_key = $parts[0] ?? '';
$meta_key = $parts[1] ?? '';

This one-line fix resolves the warnings across all ACF dynamic tag types since they all call Module::get_tag_value_field() which in turn calls Dynamic_Value_Provider::get_value() where the broken destructuring lives.

### Elementor System Info

```txt
Elementor Pro: 4.1.1 (also reproduced on 4.1.2)
WordPress: 7.0
PHP: 8.x
ACF: 6.8.4
Server: AWS EC2 / Nginx / PHP-FPM
```

### Agreement

- [x] I confirm I have read and followed all the guidelines and instructions outlined in the Elementor Bug Report form.
- [x] I agree that my issue may be closed without further action if it doesn't meet all the requirements outlined in the Elementor Bug Report form.

Start with elementor-pro/modules/dynamic-tags/acf/dynamic-value-provider.php at line 16, then trace the ACF dynamic tag callers such as acf-text.php and acf-url.php. Reproduce an ACF dynamic tag render under PHP 8.x and verify that fields whose keys lack a colon no longer emit undefined array key warnings.

Written by the indexing model from the issue text.