Upgrade to libakerror 1.0.0

Bump deps/libakerror 22 commits to 5ff8790 (1.0.0), which makes the
status-name table private, moves consumer status codes to a band starting
at AKERR_FIRST_CONSUMER_STATUS, enforces range ownership rather than
treating it as advisory, and gives the library an soname. See
deps/libakerror/UPGRADING.md.

src/stdlib.c needed no changes. This library defines no status codes of its
own -- it raises libakerror's AKERR_* codes and propagates errno, both
inside libakerror's reserved 0-255 band -- and it never referenced
AKERR_MAX_ERR_VALUE, __AKERR_ERROR_NAMES, AKERR_STATUS_RANGE_OK or
AKERR_STATUS_NAME_OK. What moved was everything around the code:

A -DAKSL_COVERAGE=ON build stopped configuring at all. libakerror
namespaces its `mutation` target when embedded but not its `coverage`
target, so it collided with ours. Shadow add_custom_target for the duration
of the add_subdirectory() call and rename the dependency's to
akerror_coverage, alongside the existing add_test shadow. Fix upstream and
delete the workaround; recorded in TODO.md.

Pin the 1.0.0 floor three ways, since no single one covers every
consumption path: an #error in akstdlib.h feature-testing
AKERR_FIRST_CONSUMER_STATUS, because libakerror publishes no version macro;
Requires: akerror >= 1.0.0 in akstdlib.pc, which also gets consumers
-lakerror transitively; and find_dependency(akerror) in
akstdlibConfig.cmake. The last was already broken before this bump -- the
template still carried its MyLibraryConfig placeholder with the dependency
commented out, so any external find_package(akstdlib) failed with a bare
"akerror::akerror not found" out of the generated targets file.

Branch coverage of src/stdlib.c fell from 51.0% to 44.3% with no source or
test change: the 1.0.0 PREPARE_ERROR/FAIL_* macros expand to more branches
at every call site, so 337/661 became 481/1087 -- 144 more branches covered,
426 more counted. Line coverage held at 99.0% (200/202) and function
coverage at 100% (21/21). Re-ratchet the CI branch gate 45 -> 40 rather than
chase branches that belong to libakerror's own suite.

tests/test_status_registry.c pins the contract that made the status-code
migration a no-op: libakstdlib reserves no consumer range, so an application
may allocate from AKERR_FIRST_CONSUMER_STATUS without coordinating with it,
and every status this library raises is inside the reserved band with a name
actually registered -- an unnamed one degrades to "Unknown Error" in every
later stack trace, which nothing else would notice. It exercises the new
ownership enforcement too, so the "reserves nothing" assertion cannot pass
vacuously.

ctest 13/13, ASan+UBSan 13/13, coverage 15/15 at 90/40, mutation 89.6%
(155/173, unchanged). Also verified out of tree: the #error fires as the
first diagnostic against a stale akerror.h, pkg-config refuses akerror
0.9.0, and an external find_package(akstdlib) consumer builds and runs
against a temp-prefix install.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

cmake/akstdlib.cmake.in

@@ -1,5 +1,17 @@
-# cmake/MyLibraryConfig.cmake.in
-include(CMakeFindDependencyMacro) # If your library has dependencies
-# find_dependency(AnotherDependency REQUIRED) # Example dependency
+# cmake/akstdlib.cmake.in -- installed as akstdlibConfig.cmake
+#
+# akstdlibTargets.cmake names akerror::akerror in the INTERFACE_LINK_LIBRARIES of
+# the imported akstdlib target, because akstdlib links it PUBLIC. Without the
+# find_dependency below, a consumer that has not already found akerror itself
+# gets a bare "target not found" out of the generated targets file rather than a
+# message naming the dependency it is missing.
+#
+# No version is requested here. libakerror installs no akerrorConfigVersion.cmake,
+# so find_dependency(akerror 1.0.0) would be refused for want of a version file
+# regardless of which akerror is actually installed. The 1.0.0 floor is carried by
+# the `Requires: akerror >= 1.0.0` line in akstdlib.pc and enforced at compile
+# time by the #error guard at the top of akstdlib.h.
+include(CMakeFindDependencyMacro)
+find_dependency(akerror)
 
 include("${CMAKE_CURRENT_LIST_DIR}/akstdlibTargets.cmake")