build: migrate to create-typescript-app@1

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🛠 Tooling: Migrate to create-typescript-app@1 #68
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Runs npx create-typescript-app --base everything --mode migrate.

Adds a bit of testing while I'm here.

[codecov]

Codecov Report

Merging #69 (00b82ad) into main (1ce7a4d) will increase coverage by 13.20%.
The diff coverage is 31.81%.

@@             Coverage Diff             @@
##             main      #69       +/-   ##
===========================================
+ Coverage   15.68%   28.88%   +13.20%     
===========================================
  Files           6        7        +1     
  Lines          51      225      +174     
  Branches        7        8        +1     
===========================================
+ Hits            8       65       +57     
- Misses         43      160      +117     

Files Changed	Coverage Δ
src/getExistingContributors.ts	0.00% <0.00%> (ø)
src/index.ts	0.00% <0.00%> (ø)
src/doesPullAlreadyHaveComment.ts	100.00% <100.00%> (+100.00%)	⬆️
src/getMissingContributions.ts	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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