Enabling lint usage and fixing static analysis error

[donpui]

Enabling lint usage and fixing static analysis error. Issue: #217

Also one fix necessary in dart_wormhole_william

I have some doubts about immutable ignore cases, maybe here requires are little bit more looking

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Code Review Checklist

• Description accurately reflects what changes are being made.
• Description explains why the changes are being made (or references an issue containing one).
• The PR appropriately sized.
• New code has enough tests.
• New code has enough documentation to answer "how do I use it?" and "what does it do?".
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