Merge bitcoin/bitcoin#25614: Severity-based logging, step 2

9580480570 Update debug logging section in the developer notes (Jon Atack)
1abaa31aa3 Update -debug and -debugexclude help docs for severity level logging (Jon Atack)
45f9282162 Create BCLog::Level::Trace log severity level (Jon Atack)
2a8712db4f Unit test coverage for -loglevel configuration option (klementtan)
eb7bee5f84 Create -loglevel configuration option (klementtan)
98a1f9c687 Unit test coverage for log severity levels (klementtan)
9c7507bf76 Create BCLog::Logger::LogLevelsString() helper function (klementtan)
8fe3457dbb Update LogAcceptCategory() and unit tests with log severity levels (klementtan)
c2797cfc60 Add BCLog::Logger::SetLogLevel()/SetCategoryLogLevel() for string inputs (klementtan)
f6c0cc0350 Add BCLog::Logger::m_category_log_levels data member and getter/setter (Jon Atack)
2978b387bf Add BCLog::Logger::m_log_level data member and getter/setter (Jon Atack)
f1379aeca9 Simplify BCLog::Level enum class and LogLevelToStr() function (Jon Atack)

Pull request description:

  This is an updated version of https://github.com/bitcoin/bitcoin/pull/25287 and the next steps in parent PR #25203 implementing, with Klement Tan, user-configurable, per-category severity log levels based on an idea by John Newbery and refined in GitHub discussions by Wladimir Van der Laan and Marco Falke.

  - simplify the `BCLog::Level` enum class and the `LogLevelToStr()` function and add documentation
  - update the logging logic to filter logs by log level both globally and per-category
  - add a hidden `-loglevel` help-debug config option to allow testing setting the global or per-category severity level on startup for logging categories enabled with the `-debug` configuration option or the logging RPC (Klement Tan)
  - add a `trace` log severity level selectable by the user; the plan is for the current debug messages to become trace, LogPrint ones to become debug, and LogPrintf ones to become info, warning, or error

  ```
  $ ./src/bitcoind -help-debug | grep -A10 loglevel
    -loglevel=<level>|<category>:<level>
         Set the global or per-category severity level for logging categories
         enabled with the -debug configuration option or the logging RPC:
         info, debug, trace (default=info); warning and error levels are
         always logged. If <category>:<level> is supplied, the setting
         will override the global one and may be specified multiple times
         to set multiple category-specific levels. <category> can be:
         addrman, bench, blockstorage, cmpctblock, coindb, estimatefee,
         http, i2p, ipc, leveldb, libevent, lock, mempool, mempoolrej,
         net, proxy, prune, qt, rand, reindex, rpc, selectcoins, tor,
         util, validation, walletdb, zmq.
  ```

  See the individual commit messages for details.

ACKs for top commit:
  jonatack:
    One final push per `git range-diff a5d5569 ce3c4c9 9580480` (should be trivial to re-ACK) to ensure this pull changes no default behavior in any way for users or the tests/CI in order to be completely v24 compatible, to update the unit test setup in general, and to update the debug logging section in the developer notes.
  klementtan:
    reACK 9580480570
  1440000bytes:
    reACK 9580480570
  vasild:
    ACK 9580480570
  dunxen:
    reACK 9580480
  brunoerg:
    reACK 9580480570

Tree-SHA512: 476a638e0581f40b5d058a9992691722e8b546471ec85e07cbc990798d1197fbffbd02e1b3d081b4978404e07a428378cdc8e159c0004b81f58be7fb01b7cba0

test/functional/test_framework/test_node.py

@@ -118,6 +118,8 @@ class TestNode():
             self.args.append("-logthreadnames")
         if self.version_is_at_least(219900):
             self.args.append("-logsourcelocations")
+        if self.version_is_at_least(239000):
+            self.args.append("-loglevel=trace")
 
         self.cli = TestNodeCLI(bitcoin_cli, self.datadir)
         self.use_cli = use_cli