feat: split Go module and build caches

Reuse downloaded modules across Go versions, runner architectures, and
runner images on the same OS instead of duplicating them in each build
cache archive.

Restore and save each entry independently, running operations in parallel
when safe. Serialize restores for overlapping or aliased paths, preserve
the original paths for the post step, and report cache-hit only when both
entries match their primary keys.

Update the documented manual restore keys and generated action bundles.

src/constants.ts

@@ -1,6 +1,5 @@
 export enum State {
-  CachePrimaryKey = 'CACHE_KEY',
-  CacheMatchedKey = 'CACHE_RESULT'
+  CacheEntries = 'CACHE_ENTRIES'
 }
 
 export enum Outputs {