perf: only register ts-node once when loading TS config files

[grxy]

Summary

Memory usage increased linearly when using multiple jest.config.ts files. This seems to have been caused by the fact that we require and register a new instance of ts-node whenever a new jest.config.ts file is encountered. By only registering one instance of ts-node, we are able to reduce memory usage significantly in multi-config projects.

Test plan

1. Made the change in this repo.
2. Ran yarn jest-ts in the issue repo
3. Added additional jest.config.ts files to the issue repo
4. Noticed that heap usage remained about the same regardless of number of jest.config.ts files

Closes #12159

[codecov-commenter]

Codecov Report

Merging #12160 (431670a) into main (2b78dd2) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main   #12160   +/-   ##
=======================================
  Coverage   67.71%   67.71%           
=======================================
  Files         328      328           
  Lines       16991    16991           
  Branches     4817     4817           
=======================================
  Hits        11506    11506           
  Misses       5452     5452           
  Partials       33       33           

Impacted Files	Coverage Δ
...ges/jest-config/src/readConfigFileAndSetRootDir.ts	2.94% <0.00%> (ø)

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[G-Rath]

Damn this didn't occur to me when I reviewed the original PR, but it makes sense - while the ts-node requiring will be cached, the register won't; sorry about that!

This looks good to me 👍

(I don't have explicit permission to make this an approve, so this'll have to do)

[SimenB]

makes a lot of sense, thanks!

[github-actions]

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