tests: add startstop condition generator testbench

fix: make sure scl changed after delay

tests: add test for scl generator

chore: get rid of "pulse" from scl names

feat: handle errors in slave state

Moves logic of error handling to slave_state
from tx entity.

feat: add unexpected_sda tx signal

refactor: get rid of sda, scl overrides, drive sda, scl directly

refactor: use 'H' std_logic state instead of custom pull up type

tests: rename startstop_condition_detector testbench to contain tb

tests: add messages to checks

tests: add pull up sda, scl behavior

tests: split master i2c functions to separata package

feat: add clear_buffer input to tx

tests: add slave testbench

fix: make slave work

feat: handle ack in rx, tx

feat(tx): remove unnecessary bit index

chore: use process(all) for combinational processes

tests: add tx testbench

tests: add rx testbench