Fix GRIB table lookup logic for multiple matching entries

Describe the Enhancement

This issue arose via GitHub discussion dtcenter/METplus#1744. Please see this comment in particular for an explanation of the issue.

Put simply, the logic for when/how both the units and long name are determined for GRIB1 and GRIB2 input data is insufficient. Currently, the MET library code uses the requested variable name, along with any other user-specified filters (e.g. GRIB2_cntr and so on), to search the GRIB tables for matches. If multiple matches are found, it just uses the first match to define the units and long name for that variable.

And that's where the problem lies. It can't actually define the units and long name until the data is actually read. Recommend refining this logic to only define the units and long name when the data is actually read rather than before it.

Time Estimate

1 day

Sub-Issues

Consider breaking the enhancement down into sub-issues. None needed.

Relevant Deadlines

List relevant project deadlines here or state NONE.

Funding Source

Define the source of funding and account keys here or state NONE.

Define the Metadata

Assignee

[ ] Select engineer(s) or no engineer required
[ ] Select scientist(s) or no scientist required

Labels

[x] Select component(s)
[x] Select priority
[x] Select requestor(s)

Projects and Milestone

[x] Select Repository and/or Organization level Project(s) or add alert: NEED PROJECT ASSIGNMENT label
[x] Select Milestone as the next official version or Future Versions

Define Related Issue(s)

Consider the impact to the other METplus components.

[x] METplus, MET, METdataio, METviewer, METexpress, METcalcpy, METplotpy No impacts.

Enhancement Checklist

See the METplus Workflow for details.

[ ] Complete the issue definition above, including the Time Estimate and Funding Source.
[ ] Fork this repository or create a branch of develop. Branch name: feature_<Issue Number>_<Description>
[ ] Complete the development and test your changes.
[ ] Add/update log messages for easier debugging.
[ ] Add/update unit tests.
[ ] Add/update documentation.
[ ] Push local changes to GitHub.
[ ] Submit a pull request to merge into develop. Pull request: feature <Issue Number> <Description>
[ ] Define the pull request metadata, as permissions allow. Select: Reviewer(s) and Linked issues Select: Repository level development cycle Project for the next official release Select: Milestone as the next official version
[ ] Iterate until the reviewer(s) accept and merge your changes.
[ ] Delete your fork or branch.
[ ] Close this issue.

dtcenter / MET