Consider a standalone Go package for Postgres WAL naming/LSN helpers

[joao00001]

Hi all 👋. While working on the sendwal extraction (#148), I ran into something worth splitting into its own proposal: SegmentFromName from github.com/cloudnative-pg/cloudnative-pg/pkg/postgres is used in three places in Klio: core/pkg/sendwal/receiver.go, core/internal/server/walserver/upload.go, and core/internal/consumer/wal.go, purely to parse a WAL segment file name back into an LSN/timeline. That's the only reason those packages pull in the full operator module as a dependency.

The reverse direction already lives in machinery (types.Int64ToLSN(...).WALFileName(tli, segmentSize), used in wal_handler.go), so there's precedent for this kind of helper being small and dependency-free — it's just that today the two directions (name → LSN and LSN → name) live in two different modules, one of which is much heavier than it needs to be for this.

I'd like to propose a small, self-contained package (no operator dependency, no I/O) covering both directions plus timeline handling, that Klio, the sendwal extraction, the CNPG operator and others could all import instead of each carrying their own copy or a heavy transitive dependency for one function.

This one is independent of the sendwal extraction itself (which is currently paused, see the note below) and looks like the simplest of the pending extraction candidates, so I'd like to start here.

Related: sendwal's extraction (#148) is currently paused, since PR #124 (dev/98) is reworking the exact write path we'd be decoupling, with an ack-based/durability redesign. Once that settles we'll pick sendwal back up; in the meantime I'd like to move on this and the other two extraction candidates (compression, encryption, opened as separate discussions) that don't have any PR in flight to conflict with.