minor #1023 [Platform][Gemini] Switch to newer gemini model supporting structured + tool call (chr-hertel)

This PR was merged into the main branch.

Discussion
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[Platform][Gemini] Switch to newer gemini model supporting structured + tool call

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Docs?         | no
| Issues        | Fix #803
| License       | MIT

Only 3 supports that again

Commits
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53b9070 Switch to newer gemini model supporting structured + tool call

Author: OskarStark

examples/gemini/structured-output-clock.php

@@ -30,7 +30,7 @@
 $clock = new Clock(new SymfonyClock());
 $toolbox = new Toolbox([$clock], logger: logger());
 $toolProcessor = new AgentProcessor($toolbox);
-$agent = new Agent($platform, 'gemini-2.5-flash', [$toolProcessor], [$toolProcessor]);
+$agent = new Agent($platform, 'gemini-3-pro-preview', [$toolProcessor], [$toolProcessor]);
 
 $messages = new MessageBag(Message::ofUser('What date and time is it?'));
 $result = $agent->call($messages, ['response_format' => [