feat: load yara lazily to avoid action dispatcher error

[Pouyanpi]

Description

implement lazy loading and improve error handling for yara dependency

• Implement lazy loading of yara module with proper type hints
• Add error messages when yara is not available
• Add helper function _check_yara_available() for consistent error handling

Related PR

#1091

Steps to Repro

# use a clean env

poetry env remove --all

# do not install `dev` dependencies 
poetry install -E "openai"

poetry run nemoguardrails chat --config="./examples/bots/hello_world"

expected output

Failed to register actions.py from nemoguardrails/library/injection_detection/actions.py in action dispatcher due to exception: No module named 'yara'
Starting the chat (Press Ctrl + C twice to quit) ...
Failed to register actions.py from nemoguardrails/library/injection_detection/actions.py in action dispatcher due to exception: No module named 'yara'

[erickgalinkin]

Looks good to me. Great catch!

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 82.35294% with 3 lines in your changes missing coverage. Please review.

Project coverage is 68.00%. Comparing base (eede896) to head (d1b7509).
Report is 52 commits behind head on develop.

Files with missing lines	Patch %	Lines
...oguardrails/library/injection_detection/actions.py	82.35%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1162   +/-   ##
========================================
  Coverage    68.00%   68.00%           
========================================
  Files          161      161           
  Lines        15793    15801    +8     
========================================
+ Hits         10740    10746    +6     
- Misses        5053     5055    +2     

Flag	Coverage Δ
python	68.00% <82.35%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...oguardrails/library/injection_detection/actions.py	78.18% <82.35%> (-0.25%)	⬇️

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[trebedea]

Looks good.

Only one suggestion, if this makes sense.
Would it be better to only have the action public and all the other functions private (seen as helpers, as they should not be used on their own - or can they be used separately)? This way we can check for availability of yara package only in the injection_detection action.

[Pouyanpi]

Looks good.

Only one suggestion, if this makes sense. Would it be better to only have the action public and all the other functions private (seen as helpers, as they should not be used on their own - or can they be used separately)? This way we can check for availability of yara package only in the injection_detection action.

Totally, very nice suggestion, thank you! And at some point we are going to strictly define our public interfaces 👍🏻