Align BlockFetch.Decision and ClientMetrics namespaces with what is emitted

[pucedoteth]

Description

Fixes #6667, taking the localized approach @mgmeier suggested there — restoring consistency across usage, documentation and configuration inside the existing pattern, rather than deriving all three from one place.

BlockFetch.Decision. Consensus.blockFetchDecisionTracer has carried TraceDecisionEvent since ouroboros-consensus-4.1.0.0, and Tracers.hs:385 wires that field, so the node emits PeersFetch and PeerStarvedUs. Both declaration sites still spelled the pre-TraceDecisionEvent type by hand:

Logging.Trace IO [BlockFetch.TraceLabelPeer remotePeer (FetchDecision [Point (Header blk)])]

whose namespaces are EmptyPeersFetch, Accept and Decline. So the three documented namespaces can never fire, and the two that do fire are unknown to checkTraceConfiguration — they cannot be re-levelled or silenced from a config file.

BlockFetch.Client.ClientMetrics had the mirror-image problem: composed onto the blockfetch client tracer in Tracers.hs:389 and documented at the ["BlockFetch","Client"] prefix, but absent from getAllNamespaces, so naming it in a configuration produced a Config namespace error.

Both sites are now annotated with the record's own type, ClientMetrics is added at the BlockFetch.Client prefix, and newNamespaces.txt is updated accordingly (Accept/Decline/EmptyPeersFetch out, PeerStarvedUs/PeersFetch in; the file stays C-locale sorted).

The Ouroboros.Network.BlockFetch.Decision import is dropped from both modules, since FetchDecision was its only use in either and cabal.project sets -Werror.

Notes for the reviewer

I could not build this. I have no GHC/cabal toolchain available, and a cardano-node build needs libsodium/secp256k1/blst besides. Rather than guess, here is what I did check statically — please let CI be the judge:

• ClientMetrics is exported from Cardano.Node.Tracing.Tracers.Consensus (export list line 21), so the new import in Consistency.hs resolves.
• No import cycle: Tracers.Consensus does not import Consistency, and it was already reachable via Consistency -> Documentation -> Tracers.Consensus.
• Dropping the Decision import is safe in both modules: FetchDecision was its only symbol in use, while Point (from Ouroboros.Network.Block) and the qualified BlockFetch. (from BlockFetch.ClientState) are still used 12x/7x and 26x respectively, so those imports stay live.
• TraceDecisionEvent is spelled exactly as Tracers/Consensus.hs:79 imports it, and applied at the arity used by the MetaTrace instance at line 657 and the consensus record field.
• Import lines follow the surrounding stylish-haskell alignment.

I have not run hlint or stylish-haskell either, for the same reason.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
  • The namespace consistency check is itself the test here: checkTraceConfiguration compares getAllNamespaces against the configuration, and newNamespaces.txt is the golden list this PR updates.
• Any changes are noted in the CHANGELOG.md for affected package
• The version bounds in .cabal files are updated — not applicable, no dependency change
• CI passes. See note above: I could not run the build or the linters locally.