GHA/checksrc: expand spellcheck, fix issues found

- codespell: break logic out into its own runnable script. Allowing
  to run it on local machines.
- codespell: install via `pip`, bump to latest version.
- codespell: show version number in CI log.
- codespell: drop no longer needed word exception: `msdos`.
- codespell: include all curl source tree, except `packages` and
  `winbuild`. Drop an obsolete file exclusion.
- add new spellchecker job using the `typos` tool. It includes
  the codespell dictionary and a couple more. Use linuxbrew to install
  it. This takes 10 seconds, while installing via `cargo` from source
  would take over a minute.
- codespell: introduce an inline ignore filter compatible with `cspell`
  Make `typos` recognize it, too. Move single exceptions inline.

Fix new typos found. Also rename variables and words to keep
spellchecking exceptions at minumum. This involves touching some tests.
Also switch base64 strings to `%b64[]` to avoid false positives.

Ref: https://github.com/crate-ci/typos/blob/master/docs/reference.md
Ref: https://github.com/codespell-project/codespell?tab=readme-ov-file#inline-ignore
Ref: https://github.com/codespell-project/codespell/issues/1212#issuecomment-1721152455
Ref: https://cspell.org/docs/Configuration/document-settings

Closes #17905

include/curl/curl.h

@@ -2750,7 +2750,7 @@ CURL_EXTERN CURLcode curl_global_init(long flags);
  * for each application that uses libcurl. This function can be used to
  * initialize libcurl and set user defined memory management callback
  * functions. Users can implement memory management routines to check for
- * memory leaks, check for mis-use of the curl library etc. User registered
+ * memory leaks, check for misuse of the curl library etc. User registered
  * callback routines will be invoked by this library instead of the system
  * memory management routines like malloc, free etc.
  */