Improve base weights consistency and make sure they're never zero (#11806)

* Improve base weights consistency and make sure they're never zero

* Switch back to `linregress` crate; add back estimation errors

* Move the test into `mod tests`

* Use all of the samples instead of only the first one

* Use full precision extrinsic base weights and slopes

* Add an extra comment

* ".git/.scripts/bench-bot.sh" pallet dev pallet_contracts

Co-authored-by: parity-processbot <>
Co-authored-by: Shawn Tabrizi <[email protected]>