Add missing builders to Mistral models to follow project patterns

[jasonparallel]

Thank you for taking time to contribute this pull request!
You might have already read the [contributor guide][1], but as a reminder, please make sure to:

• Sign the contributor license agreement
• Rebase your changes on the latest main branch and squash your commits
• Add/Update unit tests as needed
• Run a build and make sure all tests pass prior to submission

[dev-jonghoonpark]

🙌 Please fix the DCO check by signing your commit. git commit --amend --signoff @jasonparallel

[dev-jonghoonpark]

Please update license header (2024 → 2025)
(see: https://github.com/spring-projects/spring-ai/blob/main/CONTRIBUTING.adoc#update-license-header-to-modified-files-as-necessary)

/*
 * Copyright 2023-2025 the original author or authors.
 *

[dev-jonghoonpark]

Please update the existing codes(include test code) that uses constructor to use Builder.

[dev-jonghoonpark]

Could you please avoid changing the import order unless necessary? It helps maintain consistency.
Also, kindly avoid modifying the license header unless there's a specific reason.
Thank you!

[dev-jonghoonpark]

In my personal opinion, it would be better to handle the "Fix Formatter onn typos" task in a separate PR for files that are not related to the Mistral API.

[jasonparallel]

@dev-jonghoonpark
I assumed spring-javaformat:apply would put everything as it should be after the eclipse one ran but it looks like that was nto the case. I'll clean it up.

onn fix moved to #3477

[jasonparallel]

@dev-jonghoonpark Updated. Will github actions run all the IT with keys on the PR?

[dev-jonghoonpark]

@jasonparallel Good job. Let's wait for the maintainer's review.

[jasonparallel]

@dev-jonghoonpark Anyone we can ping on this?

[ilayaperumalg]

This should be resolvedApiKey. will fix when merging.

[ilayaperumalg]

@jasonparallel Thanks for the PR. Rebased, fixed the comment, and merged as b8dfc09