Alter column refactor

[Anish9901]

Fixes #4427
Fixes #4425
Fixes #4428

This refactor aims to:

• Provide better error messages to users when column alterations fail
• Improve readability of msar.alter_columns function, to enable eaiser debugging.

This is achieved in this PR by executing separate queries for alter operations rather than combining them into a giant SQL ALTER statement.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the develop branch of the repository
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

Developer Certificate of Origin

Developer Certificate of Origin

Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
1 Letterman Drive
Suite D4700
San Francisco, CA, 94129

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.


Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.

[mathemancer]

Okay, this looks good overall!

I noticed that this adds to the number of long lines (i.e., over 100 characters) in the 05_msar.sql file, but they're not the only ones. @Anish9901 Please make an issue to spend a few minutes reducing line lengths in this file. The long lines wreck my workflow, since I use psql to look at function docstrings and bodies.