Exp: import extensions

[RobinTail]

This will come handy for JSR and Node 24 bare typescript running (early available without flags in 23.6): https://nodejs.org/api/typescript.html#type-stripping

For typescript running will also need verbatimModuleSyntax

UPD: erasableSyntaxOnly from TS 5.8 can be used to ensure base typescript running

[coveralls-official[bot]]

coverage: 100.0%. remained the same when pulling c3b3db7477cd780330c68a574918a2fbc97bfb40 on import-extenstions into 74a1de9ad0eccacfe5502fb30998cb61604889b6 on master.