Use explicit ts specifiers for declarations

Restore explicit .ts relative specifiers in source and enable rewriteRelativeImportExtensions so emitted JS uses .js while declarations keep explicit .ts specifiers. Add a NodeNext declaration-consumer gate to prevent extensionless declaration regressions.

vendor/cosmokit/src/array.ts

@@ -1,4 +1,4 @@
-import { isNullable } from './misc'
+import { isNullable } from './misc.ts'
 
 /** Return true when every item in `array2` is present in `array1`. */
 export function contain(array1: readonly any[], array2: readonly any[]) {

vendor/cosmokit/src/index.ts

@@ -1,10 +1,10 @@
 /** Array set and normalization helpers. */
-export * from './array'
+export * from './array.ts'
 /** Runtime type, binary, clone, and equality helpers. */
-export * from './types'
+export * from './types.ts'
 /** Shared utility types and object helpers. */
-export * from './misc'
+export * from './misc.ts'
 /** String case, path, and property formatting helpers. */
-export * from './string'
+export * from './string.ts'
 /** Time constants, parsing, and formatting helpers. */
-export * from './time'
+export * from './time.ts'

vendor/cosmokit/src/types.ts

@@ -1,4 +1,4 @@
-import { isNullable } from './misc'
+import { isNullable } from './misc.ts'
 
 type GlobalConstructorNames = keyof {
   [K in keyof typeof globalThis as typeof globalThis[K] extends abstract new (...args: any) => any ? K : never]: K