* Enable agent context windows to be accurate per provider:model
* Refactor model mapping to external file
Add token count to document length instead of char-count
refernce promptWindowLimit from AIProvider in central location
* remove unused imports
* add LLM support for perplexity
* update README & example env
* fix ENV keys in example env files
* slight changes for QA of perplexity support
* Update Perplexity AI name
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Co-authored-by: timothycarambat <rambat1010@gmail.com>