[refactor] Rename `encodeCacheTag` to `encodeHeaderSafe` (#96936)
The helper percent-encodes anything outside Node's valid header-value
class so a string can be serialized into an HTTP header. That is a
property of the transport, not of cache tags, and the next caller is
`unstable_cache`'s synthetic `fetchUrl`, which is a cache item name
rather than a tag. Naming the function after one of its callers would
make that call site read as though it were tagging something.
This change renames the module to `encode-header-safe.ts` and the
function to `encodeHeaderSafe`, and generalizes the leading paragraph of
the doc comment accordingly. The rationale specific to cache tags stays,
since tag construction and invalidation remain the callers today. The
doc now also names the `ByteString` conversion that `fetch` performs on
header values, alongside `validateHeaderValue`; both already applied to
tags, because the Vercel bridge sends them through `fetch`.
There is no behavior change. The function body is identical apart from
the parameter name.
next.js
1f0cd93b - [refactor] Rename `encodeCacheTag` to `encodeHeaderSafe` (#96936)
