refactor: split and rename `column_operation.rs`

[iajoiner]

Please be sure to look over the pull request guidelines here: https://github.com/spaceandtimelabs/sxt-proof-of-sql/blob/main/CONTRIBUTING.md#submit-pr.

Please go through the following checklist

• [x] The PR title and commit messages adhere to guidelines here: https://github.com/spaceandtimelabs/sxt-proof-of-sql/blob/main/CONTRIBUTING.md. In particular ! is used if and only if at least one breaking change has been introduced.
• [x] I have run the ci check script with source scripts/run_ci_checks.sh.

Rationale for this change

column_operation.rs is incredibly long. It is time to split out ColumnType manipulations as a separate file. Moreover since we will most likely have a separate file for Column operations and that we don't even use either OwnedColumn or Column in column_operation.rs it is a misnomer and should be renamed slice_operation.rs. Decimal-related code is long, has unusual dependencies and can't easily be simplified hence they should be split into a separate file too.

What changes are included in this PR?

• Move ColumnType-related code to column_type_operation.rs
• Move decimal-related slice manipulation code to slice_decimal_operation.rs
• Rename the file to slice_operation.rs

  Existing tests should pass

[github-actions[bot]]

:tada: This PR is included in version 0.36.4 :tada:

The release is available on GitHub release

Your semantic-release bot :package::rocket: