init: reject -noconnect double-negatives that become -connect=1 #35939

Fixes #31426.

Motivation

-noconnect=0 is interpreted as -connect=1, which is interpreted as -connect=0.0.0.1

bitcoind -noconnect=0 -debug=net

before this change that leads to a connection attempt to 0.0.0.1 (and the usual -connect parameter interactions that disable listen/dnsseed). bitcoind should not try to connect to 0.0.0.1 from that permutation.

Change

Fail init for invalid -noconnect values, same pattern as -wallet / -nowallet: -connect must be a string host/IP -noconnect / -noconnect=1 still disable automatic connections

Double-negatives like -noconnect=0 are stored as boolean true, which GetArgs stringifies as "1" and Lookup resolves as 0.0.0.1

those now error instead.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35939.

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