Introduce generics to splay

[sejongk]

What this PR does / why we need it:

Introduce generics to splay

Which issue(s) this PR fixes:

Fixes #304

Special notes for your reviewer:

By introducing generics to splay, we don't have to use the type assertions in RGATreeSplit and RGATreeList.
If there is anything that needs improvement, please let me know. :)

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[CLAassistant]

All committers have signed the CLA.

[hackerwins]

@sejongk Thanks for your contribution.
Please check the lint errors on the CI.

[hackerwins]

Looking at the lint errors, it is thought to be the lint malfunction. 🤔
I changed the Node to the same receiver name as Tree to avoid it for now.

[codecov]

Codecov Report

Merging #346 (43e44ab) into main (aea0304) will not change coverage.
The diff coverage is 84.21%.

@@           Coverage Diff           @@
##             main     #346   +/-   ##
=======================================
  Coverage   48.30%   48.30%           
=======================================
  Files          65       65           
  Lines        5473     5473           
=======================================
  Hits         2644     2644           
  Misses       2551     2551           
  Partials      278      278           

Impacted Files	Coverage Δ
pkg/splay/splay.go	87.95% <80.00%> (ø)
pkg/document/json/rga_tree_list.go	64.28% <100.00%> (ø)
pkg/document/json/rga_tree_split.go	75.00% <100.00%> (ø)

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[sejongk]

@hackerwins Thanks for your edit.

Looking at the lint errors, it is thought to be the lint malfunction.

I totally agree with you. I will check whether the linter is working properly and share related information if the current linter's upgrade is necessary.

[sejongk]

@hackerwins It seems a bug in the revive module enabled in golangci-lint, and the bug is fixed (ref. mgechev/revive#692).
When golangci-lint bumps up its revive to the new version that includes the patch, we may resolve the above problem by upgrading golangci-lint.