feat: allow to pass "none" as reasoning effort

[Danidapena]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

allows to set reasoning effort to node so it can be turned of on gemini models

from litai import LLM 

llm = LLM(model='google/gemini-2.5-flash-lite-preview-06-17')

response = llm.chat("think about energy",  max_tokens=1, reasoning_effort='none')
print(response)

response

Energy

Fixes # (issue).

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in GitHub issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84%. Comparing base (00a3eca) to head (441f87c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@        Coverage Diff         @@
##           main   #64   +/-   ##
==================================
  Coverage    84%   84%           
==================================
  Files         8     8           
  Lines       466   466           
==================================
  Hits        390   390           
  Misses       76    76           

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[k223kim]

Thank you @Danidapena 🔥