refactor: use jiti.import for esm stubs and improve templates

[antfu]

requires unjs/jiti#158

[pi0]

(drafting until we support jiti.import)

[pi0]

Updated implementation to allow iterating. From what i extracted for now and need to do in next steps

• We need to resolve jiti's esm entry path for esm (and avoid windows path to url normalization for vite support?)
• We need to pass native _import implementation to jiti.import