Update kotlinx-datetime library to 0.7.1

[OKatrych]

This update requires the latest Kotlin and serialization version to build. Also, the new library version requires opt-in to ExperimentalTime.

This is an example of a fix for https://github.com/JetBrains/koog/issues/725. I don't know which way you want to implement opt-in for ExperimentalTime, so I'm leaving this up to you.

Motivation and Context

When the application has the kotlinx-datetime library version that is less than 0.7.1 it crashes in runtime with this error:

 java.lang.NoSuchMethodError: No direct 
  method <init>(Ljava/lang/String;Lai/koog/prompt/executor/clients/anthr
  opic/AnthropicClientSettings;Lio/ktor/client/HttpClient;Lkotlin/time/C
  lock;ILkotlin/jvm/internal/DefaultConstructorMarker;)V in class 
  Lai/koog/prompt/executor/clients/anthropic/AnthropicLLMClient; or its 
  super classes (declaration of 
  'ai.koog.prompt.executor.clients.anthropic.AnthropicLLMClient' appears
   in /data/app/~~lkg4QDVldpi-pI2a0vafMQ==/dev.olek.lmclient.androidApp-
  NNRKrh5iHDxg8pT_BM3UCw==/base.apk)

Breaking Changes

This requires users to opt in for ExperimentalTime too.

Type of the changes

• [ ] New feature (non-breaking change which adds functionality)
• [ x] Bug fix (non-breaking change which fixes an issue)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation update
• [ ] Tests improvement
• [ ] Refactoring

Checklist

• [x] The pull request has a description of the proposed change
• [x] I read the Contributing Guidelines before opening the pull request
• [x] The pull request uses develop as the base branch
• [x] Tests for the changes have been added
• [ ] All new and existing tests passed

Additional steps for pull requests adding a new feature

• [ ] An issue describing the proposed change exists
• [ ] The pull request includes a link to the issue
• [ ] The change was discussed and approved in the issue
• [ ] Docs have been added / updated