gocognit split: token/services/ttx #2382

Part of #2377.

Re-apply the gocognit complexity-reduction extraction for token/services/ttx, removing the temporary //nolint:gocognit // TODO(#2377) markers #2327 leaves on this package.

Note: this package had the one real regression found on #2327 (a dropped attestation-signing call in recipients.go's exchangeRemotely extraction, caught by the itest matrix). The corrected version of that extraction is already worked out and itest-verified on the lint/enable-gocognit branch; re-review it carefully given the history.

Files in scope:

• token/services/ttx/collectendorsements.go
• token/services/ttx/recipients.go
• token/services/ttx/marshaller.go
• token/services/ttx/finality.go
• token/services/ttx/endorse.go
• token/services/ttx/endorse_opts.go
• token/services/ttx/finality/recovery.go
• token/services/ttx/finality/listener.go
• plus associated *_test.go files touched only for split subtests (endorse_test.go, finality_test.go)