Enhance the IDL Test Harness

[mwinkel-dev]

Affiliation MIT PSFC (but based on feedback from GA)

The first version of the "IDL Test Harness" (see PR #2643) has 19 tests that cover many basic features of the IDL API. But lacks a test of writing data to a tree.

The "IDL Test Harness" will be enhanced to include the following:

• add test cases to write data to trees
• add more read test cases
• for test cases based on Issues / PRs, add a comment that has a URL for the associated Issue or PR
• Provide testing across versions: (Initially for IDL, and eventually for all thin client APIs)
  • Test each client build against an old server (roughly 7.96.9)
  • Test an old client (roughy 7.96.9) against each server build

[mwinkel-dev]

On 6-Nov-2023, completed the following:

• Added an IDL test case that reads various nodes (ASCII, numeric, signal), various paths (full, relative, tag), GETNCI metadata (with wildcard path, and normal path), and other (rank, ndims, dim_of, units_of).
• Updated the existing 19 IDL tests with comments that have the URL to the associated GitHub issues.
• Inserted visual separator comment lines so easier to see where one test case ends and another begins.
• Confirmed that the existing 19 IDL tests cover these features of the IDL API: connect, disconnect, open, close, a smidgen of TDI, connect to database, and execute SQL.

Now working on a prototype of the IDL write (aka store) tests, similar to the expanded read tests.

When done with the above, will submit to GitHub as a "work in progress" PR.