move signal ignore out of `eth/common`

[arnetheduck]

net/nat is the only place where it is used and it certainly doesn't belong in common

[tersec]

 [NimScript] exec: nim c  --styleCheck:usages --styleCheck:error --verbosity:0 --hints:off --skipUserCfg --nimcache:build/nimcache -f --warning[ObservableStores]:off -d:nimOldCaseObjects -d:chronicles_log_level=TRACE --threads:on -d:release  --mm:refc -r --outdir:build/p2p tests/p2p/all_tests
/Users/runner/work/nim-eth/nim-eth/eth/p2p/rlpx.nim(972, 1) template/generic instantiation of `p2pProtocol` from here
/Users/runner/work/nim-eth/nim-eth/eth/p2p/rlpx.nim(978, 14) template/generic instantiation of `append` from here
/Users/runner/work/nim-eth/nim-eth/eth/rlp/writer.nim(311, 15) template/generic instantiation of `appendImpl` from here
/Users/runner/work/nim-eth/nim-eth/eth/rlp/writer.nim(159, 11) template/generic instantiation of `append` from here
/Users/runner/work/nim-eth/nim-eth/eth/rlp/writer.nim(311, 15) template/generic instantiation of `appendImpl` from here
/Users/runner/work/nim-eth/nim-eth/eth/rlp/writer.nim(296, 7) template/generic instantiation of `appendRecordType` from here
/Users/runner/work/nim-eth/nim-eth/eth/rlp/writer.nim(293, 21) template/generic instantiation of `enumerateRlpFields` from here
/Users/runner/work/nim-eth/nim-eth/eth/rlp/object_serialization.nim(17, 9) template/generic instantiation of `op` from here
/Users/runner/work/nim-eth/nim-eth/eth/rlp/writer.nim(291, 13) template/generic instantiation of `append` from here
/Users/runner/work/nim-eth/nim-eth/eth/rlp/writer.nim(308, 16) Warning: Signed integers cannot reliably be encoded using RLP [User]
/Users/runner/work/nim-eth/nim-eth/eth/p2p/peer_pool.nim(112, 57) template/generic instantiation of `async` from here
/Users/runner/work/nim-eth/nim-eth/eth/p2p/peer_pool.nim(152, 12) template/generic instantiation of `setResult` from here
/Users/runner/work/nim-eth/nim-eth/eth/p2p/peer_pool.nim(133, 25) Error: type mismatch
Expression: inc(rlpx_connect_success)
  [1] rlpx_connect_success: typedesc[IgnoredCollector]

Expected one of (first mismatch at [position]):
[1] func inc(a: var StInt; w: Word = 1)
[1] func inc(a: var StUint; w: Word = 1)
[1] proc inc(address: var TransportAddress; v: int = 1)
[1] proc inc[A](t: CountTableRef[A]; key: A; val = 1)
[1] proc inc[A](t: var CountTable[A]; key: A; val = 1)
[1] proc inc[T, V: Ordinal](x: var T; y: V = 1)

which is presumably because the import/export network dropped metrics here but it was never the right place to pull it in

if peer_pool wants metrics, it should import metrics itself

[arnetheduck]

if peer_pool wants metrics, it should import metrics itself

turns out it's using public gauges declared in: eth/p2p/rlpx.nim