feat: add Perplexity AI provider support with token limits and streaming

## CHANGES

- feat: Add `MaxTokens` field to `ChatOptions` struct for response control
- feat: Integrate Perplexity client into core plugin registry initialization
- build: Add perplexity-go/v2 dependency to enable API interactions
- feat: Implement stream handling in Perpexlty client using sync.WaitGroup
- fix: Correct parameter types for penalty options in API requests
## LINKS

<https://github.com/sgaunet/perlexipty-go> - Client library used

go.sum

@@ -202,6 +202,8 @@ github.com/sashabaranov/go-openai v1.40.1/go.mod h1:lj5b/K+zjTSFxVLijLSTDZuP7adO
 github.com/scylladb/termtables v0.0.0-20191203121021-c4c0b6d42ff4/go.mod h1:C1a7PQSMz9NShzorzCiG2fk9+xuCgLkPeCvMHYR2OWg=
 github.com/sergi/go-diff v1.4.0 h1:n/SP9D5ad1fORl+llWyN+D6qoUETXNZARKjyY2/KVCw=
 github.com/sergi/go-diff v1.4.0/go.mod h1:A0bzQcvG0E7Rwjx0REVgAGH58e96+X0MeOfepqsbeW4=
+github.com/sgaunet/perplexity-go/v2 v2.8.0 h1:stnuVieniZMGo6qJLCV2JyR2uF7K5398YOA/ZZcgrSg=
+github.com/sgaunet/perplexity-go/v2 v2.8.0/go.mod h1:MSks4RNuivCi0GqJyylhFdgSJFVEwZHjAhrf86Wkynk=
 github.com/sirupsen/logrus v1.7.0/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
 github.com/skeema/knownhosts v1.3.1 h1:X2osQ+RAjK76shCbvhHHHVl3ZlgDm8apHEHFqRjnBY8=
 github.com/skeema/knownhosts v1.3.1/go.mod h1:r7KTdC8l4uxWRyK2TpQZ/1o5HaSzh06ePQNxPwTcfiY=