tests: add slave testbench

fix: correct delay pulses length

fix: make slave work

feat: add slave top

feat: handle ack in rx, tx

feat(tx): remove unnecessary bit index

chore: add direnv file

tests: add vunit run.py

feat: add stateful sda, scl switch

chore: use process(all) for combinational processes

tests: add tx testbench

fix: tx bugs

feat(rx): make rx idle on start/stop condition

tests: add rx testbench

fix(rx): stretching behavior

refactor(rx): do not use unnecessary index

chore: use integer instead of natural when with range

fix: make rx properly working

feat: add possibility for 0 delay in delay entity

tests: add startstop condition detector tests, fix behavior