Merge bitcoin/bitcoin#34905: Update string and net utils for future HTTP operations

0e712b3812 Make DynSock accepted sockets queue optional, with precise lifetime (Matthew Zipkin)
3de02abf3f util/test: Add string_view constructor to LineReader and remove StringToBuffer (Matthew Zipkin)
b0ca400612 string: replace AsciiCaseInsensitiveKeyEqual with CaseInsensitiveEqual (Matthew Zipkin)
8172099293 util: get number of bytes consumed from buffer by LineReader (Matthew Zipkin)

Pull request description:

  This is a follow-up to #34242 and is the first few commits of #32061

  As review and refinement of the replacement HTTP server progresses, some new utilities were needed and added. This PR updates those utilities as work continues on #32061.

  ### LineReader

  In order to enforce strict limits on the total size of headers in HTTPRequest, we add a method to `LineReader` to give us the total amount of data that has been read from the buffer so far. See https://github.com/bitcoin/bitcoin/pull/32061#discussion_r2949287329

  ### CaseInsensitiveEqual

  HTTP headers are case-insensitive. An early version of #32061 used an unordered_map for this and therefore we needed a comparator struct. However that unordered_map was replaced by a simpler `std::vector` of `std::pair` so we can remove the struct and use methods that already exist in the codebase.

  ### StringToBytes

  `StringToBuffer` was introduced in #34242 to test LineReader but review of #32061 indicated that it would be more optimal to return a span of bytes instead of a vector. See https://github.com/bitcoin/bitcoin/pull/32061#discussion_r2892431378

  ### Split DynSock constructor for two usecases: listening / accepting sockets

  See https://github.com/bitcoin/bitcoin/pull/32061#discussion_r2895891437. DynSock was introduced in #30988 and is not used anywhere in master yet. If it's used as a listening socket, it provides connected sockets. If it's used as a connected socket, it provides I/O pipes. By making the queue of connected sockets optional we can clean up the ownership / lifetime if the class members.

ACKs for top commit:
  fjahr:
    Code review ACK 0e712b3812
  vasild:
    ACK 0e712b3812

Tree-SHA512: 234c79a00c03cb3952dce2a3c5e59859bd0cbfc5f0a552ad2065e998320a12b533b06adbe294745c690a9e19c2f5f79bca3aa5a44342ee1820037342799566f2

src/test/fuzz/bech32.cpp

@@ -5,7 +5,6 @@
 #include <bech32.h>
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/FuzzedDataProvider.h>
-#include <test/util/str.h>
 #include <util/strencodings.h>
 
 #include <cassert>