Clean ListOutputConverter responses with the shared ResponseTextCleaner

[anjeongkyun]

Builds on #6941, which adds ResponseTextCleaner.defaultCleaner(). Only the last commit here is new.

ListOutputConverter doesn't clean the response at all, so a fenced list comes back with the markers as elements:

"```\nfoo, bar, baz\n```"     -> [```, foo, bar, baz, ```]
"```csv\nfoo, bar, baz\n```"  -> [```csv, foo, bar, baz, ```]
"<think>reasoning</think>\nfoo, bar, baz" -> [<think>reasoning</think>\nfoo, bar, baz]

It fails more quietly than the Map case in #6941: no exception, just extra elements in the caller's list.

I mentioned this in #6941 and left it out because every cleaner in the chain trims, and csvWithOnlyWhitespace asserts that " \t\n " converts to a single blank element rather than an empty list. That turned out to be avoidable: cleaning only when the cleaned text is non-empty keeps the blank case on the original string, so that test passes unchanged.

String cleaned = this.textCleaner.clean(text);
if (cleaned != null && !cleaned.isEmpty()) {
    text = cleaned;
}

No existing test needed changing. The four new cases fail before the change with the markers present in the list, and mvn -pl spring-ai-model test is green (790 tests).