Remove three @ts-expect-errors for mapping types

[anderium]

This does some hacky things to get inference that works for the mapping types. Based on: https://github.com/microsoft/TypeScript/pull/47109

Also adds two comments where the expect error cannot reasonably be removed (as far as I can see).

Experiment with it here: https://www.typescriptlang.org/play?ts=5.3.3#code/C4TwDgpgBAYglgJwgEwPKQQQ2HA9gOygF4oBvKUSALigCIAzRFWgGigGMIAbLm-AVwC2AIwgIoAXwBQlaAFlcANxTox2PIRLlZNWoKXM2nHnyGiEbMLgDOcHARoBtASLFsX5gLqSZ4aKqx7TVgmNAx1AigAHygFZTC1IKlkgHoUij8oAIjg8kYkZBpUQTsAHngC7KC2WllaAD42fXiikuBSuJVw6ro6+skAbl9ILO6NABVMkiqNR1q-Wk9k2VHEjTlMMFKAaSgIAA9gCHxka1XAib9+rShHAAUoOEJtzxpSKShPjOooO5YpCRQABkWTapQAoocsOx2jMCGxSDpfhJGr0FvUAY4XkNhtAYPx8DD1psdntDsdTuccpNINcyB8vvdHs9XlAABS4MYOKlBDZbO71ACUxH6ilwcGQAOS7AI1mAUHoBKJBD5NHxhN5JLh+BpEDp7y+CtCNDZ+RQAH1OWtuRUutb8IKaGKJSL6YbDWbkJaufgAHTGLgMz4Sf6G5ooE3hr1Wi7czoJWMOp3i5Cug3uz5R732-3cQMZzMGaM+31WWxJQ3SaRSRUajRQTZgLggbWkg5HE5nbW6+ocn1FH18nZC5Mu9OfGX4OVQfbEKAxnK+2RBjiy+W19hzjeasCOfZLD1Kvv2wVSoA

I had a lot of fun trying to understand what's going on with this solution, it's bizarre that it works.

For some reason, the explicit {type: …} & Omit<…, "type"> is necessary. I still don't know why.