feat(TableRouteValue): add panic notes and type checks

[AntiTopQuark]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

add panic notes and type checks for TableRouteValue

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

Refer to a related PR or issue link (optional)

#3016

[WenyXu]

There may be some misunderstanding. Add a panic! Here is not helpful. Without this panic!, it also will panic if the table_route is not the TableRouteValue::Physical

fn physical_table_route(&self) -> &PhysicalTableRouteValue {
        match self {
            TableRouteValue::Physical(x) => x,
            _ => unreachable!("Mistakenly been treated as a Physical TableRoute: {self:?}"),
        }
}

We should add a check before calling the methods like region_routes.

i.e.,

    ensure!(
        table_route.is_physical(),
        error::UnexpectedTableRouteTypeSnafu {}
     );
    // We should check the safety before calling a method with a panic note.
    let region_route = table_route.region_routes();

BTW, this doc may be helpful.

[AntiTopQuark]

I added some error definitions and checks, following some comments given by the compiler. I'm not quite sure now if these are compliant with the greptime coding specification. Could you please check again and I'll fix it if there are any problems?
Thank you very much.

[evenyag]

Hi, we are going to switch to the main branch, as mentioned in #3025.

I have changed the target branch of this PR to main.

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (485a91f) 85.71% compared to head (bafa459) 85.18%.

❗ Current head bafa459 differs from pull request most recent head d71c3d9. Consider uploading reports for the commit d71c3d9 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3023      +/-   ##
==========================================
- Coverage   85.71%   85.18%   -0.54%     
==========================================
  Files         791      786       -5     
  Lines      127884   127363     -521     
==========================================
- Hits       109615   108489    -1126     
- Misses      18269    18874     +605     

[evenyag]

You could merge the main branch instead of the develop branch. You could rename the develop branch to main in your forked repo via GitHub UI.

[AntiTopQuark]

done, I submit a new PR:
#3031