Introduce `checked_div` for `PerThings` and `checked_rational_mul_correction`

[Gioyik]

Fixes paritytech/polkadot-sdk#199

Introduces checked_div and checked_rational_mul_correction

Notes:

• checked_div() in PerThings have to options to complete the division, however, I am not sure which one would be the best, both seem to output the same.
• The checked behavior of checked_rational_mul_correction can be introduced for multiply_by_rational_with_rounding, however it implies changing all the tests and developers using it might need to change it to expect Option<u128> instead of u128. So I am holding changes if this is not desired.

[Gioyik]

there are many panic! in the fixed_point.rs file that I think can be moved to the safe and unchecked_ function logic.

@ggwpez do you think it's fine to make the switch in those files and include it in this PR or those should stay as panic!?

[kianenigma]

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[Gioyik]

now there are checked_ functions with Result<>. One question, in these two calls:

https://github.com/paritytech/substrate/blob/gio/checked_fn/primitives/arithmetic/src/per_things.rs#L482 https://github.com/paritytech/substrate/blob/gio/checked_fn/primitives/arithmetic/src/per_things.rs#L495

do we want to replace with the checked version of the function?

[paritytech-cicd-pr]

The CI pipeline was cancelled due to failure one of the required jobs. Job name: test-linux-stable Logs: https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/3321459

[paritytech-cicd-pr]

The CI pipeline was cancelled due to failure one of the required jobs. Job name: test-linux-stable-int Logs: https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/3321465