chore(codegen): index tests and type imports

[kuhe]

Issue

JS-6374

smithy-lang/smithy-typescript@f8bed21...e11f749

Description

This applies code generation changes for:

• type imports & import ordering/grouping
• generated index tests
• well-formatted typescript (feat(codegen): generate well-formatted TypeScript source code smithy-lang/smithy-typescript#1780)
• release target is Dec 8th, 2025

The projected build time increase is:

• +20s additional type check time for all clients type index exports
• +3s index test for exported runtime objects for all clients

for a total of approximately +23s.

Testing

CI and new generated index tests

[kuhe]

notes:

JSv3 codegen time without lint/format - 7m30s (remote machine)
JSv3 codegen time with lint/format - 9m44s (remote machine)