avoid pointless exception raising in dcutr/server

[etan-status]

dcutr/server is the only protocol handler outside tests / examples that raises exceptions. The only caller of this handler is defined in MultStreamSelect.handle, which has a surrounding except block that catches CatchableError.

When the handler raises a non-CancelledError the flow is:

1. await protocolHolder.protocol.handler(conn, ms)
2. The finally block after it
3. The return, both in successful and in exception case
4. The outer except CatchableError as exc:, it logs and discards exc
5. The outer finally: await conn.close()
6. Stopped multistream handler log, both in successful and exc case.

By changing dcutr/server to only log but not also raise, difference is that the outer except CatchableError in step (4) is skipped.

As that is a redundant log anyway (dcutr/server already logs), it should be fine to not raise. That's in line with all the other protocol handlers (besides tests / examples) and opens up limiting {.raises.} annotation for handlers to just [CancelledError].

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 82.57%. Comparing base (08a48fa) to head (869d199).

Additional details and impacted files

@@            Coverage Diff            @@
##           unstable    #1063   +/-   ##
=========================================
  Coverage     82.56%   82.57%           
=========================================
  Files            91       91           
  Lines         15814    15812    -2     
=========================================
- Hits          13057    13056    -1     
+ Misses         2757     2756    -1     

Files	Coverage Δ
libp2p/protocols/connectivity/dcutr/server.nim	80.00% <50.00%> (-0.86%)	⬇️

... and 2 files with indirect coverage changes