Add typos checks and fix typos it found

[philderbeast]

I'd recently fixed many typos in haskell/cabal using the typos tool, see https://github.com/haskell/cabal/pull/10613 and https://github.com/haskell/cabal/pull/10603. I tried the tool here and found many typos.

There's already pull request #558 that fixes issue #560.

I've read the contributing notes and annotated commits with #560 but can change this issue reference to another if you want to raise one or more separate issues.

As for the GitHub action, this is using the makefile not the typos action that I tried, the same as we're using with haskell/cabal. I could get their action to work for ./**/*.md files but not ./**/*.hs files even though both work locally.

I haven't added CHANGELOG entries as I'm not yet sure if you'd like this pull request to remain whole or split up. As it is now, it touches copilot-c99, copilot-interpreter, copilot-language, copilot-theorem and copilot/examples (for which there isn't a CHANGELOG).

$ tree -P 'CHANGELOG' --prune
.
├── copilot
│   └── CHANGELOG
├── copilot-c99
│   └── CHANGELOG
├── copilot-core
│   └── CHANGELOG
├── copilot-interpreter
│   └── CHANGELOG
├── copilot-language
│   └── CHANGELOG
├── copilot-libraries
│   └── CHANGELOG
├── copilot-prettyprinter
│   └── CHANGELOG
└── copilot-theorem
    └── CHANGELOG