[mayankdhingra02]

Adding the first type parameters to an arrow function throws NotImplementedError. Insert them before the parameter list, adding parentheses around a bare parameter when needed. Preserve cached parameter and identifier nodes so later renames still work.

Single type parameters in TSX get a trailing comma to avoid being parsed as JSX. Regressions cover ordinary and async arrows, comments, existing generics, TSX, cached-node renames, and unchanged input for empty additions or invalid indices.

Fixes #1680.

Validation on TypeScript 6.0.2:

• Full package suites: 5,406 passing, 2 pending; 45 focused tests pass.
• Node and Deno builds, project type checks, code verification, and formatting pass.
• Deno smoke tests: 2 passed; package publish dry run passes.

[mayankdhingra02]

Could a maintainer approve the pending CI run when convenient? The local package tests, Node and Deno builds, type checks and formatting passed, as documented in the PR description. Thanks.