Add support for negative logging categories in the log gateway

[ZayanKhan-12]

Closes #338

Implements the enhancement suggested in #338: categories prefixed with ! in the logging_categories setting specify messages that should not be written to the error log.

Semantics

• A negative match takes precedence over any positive match, so a message tagged both send_query_ws_events and access is suppressed by ["send_query_ws_events", "!access"].
• When only negative categories are specified, all other messages remain pertinent — so ["!access"] means "everything except access", which makes the feature usable on its own.
• Existing behaviour is unchanged when logging_categories is omitted (everything logged), explicitly empty (nothing logged), or contains only positive categories, including the empty-string entry that selects messages with no category.

The settings schema already accepts these values (stringArray), and the logging_categories comment in nmos/settings.h is updated to document the prefix.

Testing

New nmos/test/log_gate_test.cpp covers all the cases above via a small log_gate subclass (20 assertions). Full local run: all 169 test cases / 2361 assertions pass (macOS arm64, apple-clang, conan dependencies per conanfile.txt).

Two environment notes from getting the suite running on an arm64 Mac, in case they're useful for #506:

• vendored third_party/catch/catch.hpp needs an __aarch64__ branch for CATCH_TRAP() (int $3 doesn't assemble on arm64) and an unsigned RandomNumberGenerator::result_type for modern libc++ — happy to submit separately if of interest;
• Boost 1.90 removes the (long header-only) Boost.System stub entirely, so find_package(Boost COMPONENTS system ...) fails against current Boost — dropping system from FIND_BOOST_COMPONENTS works fine with 1.83+.

🤖 Generated with Claude Code

[garethsb]

Nice, focused change that matches #338. I recommend a few small tweaks before merge.

1. Align example config comments
nmos-cpp-node/config.json and nmos-cpp-registry/config.json still only describe the include form. Please mirror the updated settings.h wording with one extra line on the ! prefix (and the “only excluded categories ⇒ everything else included” behaviour).

2. Treat "!" as negated ""
Today "!" is classified as negative (so it can enable “negation-only” mode) but the empty-categories path only looks for "", so "!" never excludes uncategorized messages and is effectively a no-op.

Suggestion: in the categories.empty() branch, if "!" is present return false (negative wins), else keep default_pertinent || has "". That makes the prefix rule complete and allows useful configs such as ["!"] (everything except uncategorized) and ["!", "!access"].

3. Extra test
Please add a case for ["access", "!access"] (negative wins over the same positive), and for "!" excluding uncategorized once (2) is in.

4. CI
There are no checks reported on this branch yet. @lo-simon please could you allow workflows to run?

Thanks also for the Catch/Boost notes for #506...

• I'm surprised about the need for __aarch64__ as I thought this has been built on Linux arm64 and that there was a current macOS runner 🤔
• we have bigger issues with recent Boost (since Asio deprecated API has been removed) but this sounds like an easy win in another PR