Consolidate Neptune and RDS backends

[bpandola]

Despite being documented as two distinct services (with two distinct boto3 clients), the Neptune and RDS services share a single AWS backend (RDS). This is reflected in the botocore service definition for Neptune, which lists rds as its endpoint. Calling the DescribeDBClusters API method with either the neptune or rds boto3 client results in the exact same list of clusters--no filtering is done on the AWS backend. Neptune clusters are commingled with Aurora clusters.

@bblommers I think this makes more sense than trying to separate these services (and it prevents a lot of code duplication), but I want to get your opinion since you originally implemented/split out the Neptune service. (As I continue to work on improving the RDS backend overall, I do plan to handle some of the if self.engine == "neptune conditionals in a more elegant way.)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.39%. Comparing base (bbcfc4c) to head (e5bbeab).
Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7925      +/-   ##
==========================================
+ Coverage   94.38%   94.39%   +0.01%     
==========================================
  Files        1114     1109       -5     
  Lines       95224    95084     -140     
==========================================
- Hits        89875    89758     -117     
+ Misses       5349     5326      -23     

Flag	Coverage Δ
servertests	29.13% <35.29%> (-0.03%)	⬇️
unittests	94.36% <100.00%> (+0.01%)	⬆️

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[bblommers]

@bpandola It is much cleaner like this, with RDS handling everything. If I remember correctly, I did try this approach first, but ran into some problems differentiating when a call came from Neptune and when from RDS. I don't remember exactly what went wrong, but based on this PR, it does work, so I'm more than happy to go ahead with this approach.

[bblommers]

Aside from the cache note, this looks good to me.

We would need to find a different approach for the implementation coverage script, to document that RDS coverage == Neptune coverage.
That doesn't have to be now, or even as part of this PR, just noting it as an FYI.

[bpandola]

@bblommers

We would need to find a different approach for the implementation coverage script, to document that RDS coverage == Neptune coverage. That doesn't have to be now, or even as part of this PR, just noting it as an FYI.

Good catch. I did push an additional commit to fix the implementation coverage script (it was failing before). I think it should work fine now, with no additional work required.

[github-actions]

This is now part of moto >= 5.0.12.dev64