Changed slcan serial read routine to be faster and to manage the buffer more carefully (#2028)

* Changed slcan serial read routine to be faster and to manage the buffer more cauciously

* As per merge request suggestion

Co-authored-by: zariiii9003 <52598363+zariiii9003@users.noreply.github.com>

* as per merge request suggestion

Co-authored-by: zariiii9003 <52598363+zariiii9003@users.noreply.github.com>

* Simplified slcan serial reading

* Added news fragment

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Co-authored-by: Aaron Fulton <aaron@webtolife.software>
Co-authored-by: zariiii9003 <52598363+zariiii9003@users.noreply.github.com>