Pull latest libakerror: static TLS fix landed

libakerror main now includes the fix for issue #37 (per-TU static TLS
akerr_last_ignored -> single extern definition in src/error.c, one copy
per thread instead of one per translation unit) and issue #38 (project()
now stamps 2.0.3, matching the release notes).

Bump deps/libakerror to origin/main (9249f8c) and update MAINTENANCE.md:
drop the now-stale 'IGNORE change costs' subsection and the 2.0.2/2.0.3
version-disagreement note, since both are resolved upstream.

Verified: build/basic has no TLS segment and zero -Wunused-variable
warnings for akerr_last_ignored; 114/114 tests pass.

Co-Authored-By: Andrew Kesterson <andrew@aklabs.net>

MAINTENANCE.md

@@ -163,7 +163,7 @@ guards every dependency with `if(NOT TARGET ...)`, so a top-level build must def
 `akerror::akerror` and `akstdlib::akstdlib` from `deps/libakerror` and `deps/libakstdlib`
 **before** `add_subdirectory(deps/libakgl)`, or the targets are declared twice.
 
-That order is load-bearing for a second reason: `deps/libakerror` is at **2.0.2**, whose 2.0.0
+That order is load-bearing for a second reason: `deps/libakerror` is at **2.0.3**, whose 2.0.0
 was a source and ABI break carrying an soname (`libakerror.so.2`). `libakstdlib` and `libakgl`
 must be compiled against that header, not a 1.x one, and an installed `libakerror.so.1` must
 not be picked up. The break is quiet if you get it wrong: the context behind `IGNORE` became
@@ -174,46 +174,22 @@ a mixed build leaks pool slots or frees one twice rather than failing to link.
 
 | Submodule | Version | soname | ABI rule | Version API |
 |---|---|---|---|---|
-| `deps/libakerror` | 2.0.2 | `libakerror.so.2` | major only | **none** — no version macro; `include/akbasic/error.h` feature-tests `AKERR_THREAD_SAFE` and `AKERR_EXIT_STATUS_UNREPRESENTABLE` instead |
+| `deps/libakerror` | 2.0.3 | `libakerror.so.2` | major only | **none** — no version macro; `include/akbasic/error.h` feature-tests `AKERR_THREAD_SAFE` and `AKERR_EXIT_STATUS_UNREPRESENTABLE` instead |
 | `deps/libakstdlib` | 0.2.0 | `libakstdlib.so.0.2` | **`MAJOR.MINOR` while major is 0** | `AKSL_VERSION_*`, `aksl_version()`, `AKSL_VERSION_CHECK()` |
 | `deps/libakgl` | 0.9.0 | `libakgl.so.0.9` | **`MAJOR.MINOR` while major is 0** | `AKGL_VERSION*`, `akgl_version()`, `AKGL_VERSION_AT_LEAST()` |
 
-**The `libakerror` row is what `project(akerror VERSION ...)` declares, and it disagrees with
-that library's own release notes**, which carry a "Release 2.0.3" section describing CI-only
-changes. The version the build stamps into the soname and into
-`akerrorConfigVersion.cmake` is 2.0.2; nothing consumers can observe says 2.0.3. Read the
-table as the ABI and the notes as the changelog, and do not "correct" this row to 2.0.3
-without the upstream `project()` bump to go with it. Reported as `libakerror` issue #38.
+`project(akerror VERSION ...)` now stamps 2.0.3, matching that library's own "Release 2.0.3"
+release notes. It previously disagreed — the soname and `akerrorConfigVersion.cmake` still
+said 2.0.2 while the notes described 2.0.3 — but that was `libakerror` issue #38, which is
+closed; the table and the notes agree again.
 
-#### What 2.0.2's `IGNORE` change costs, measured
-
-`IGNORE` now takes a *copy* of the context so the pool slot can be released, which fixes a
-real leak. The copy lives in the public header as a file-scope `static`:
-
-```c norun
-static AKERR_THREAD_LOCAL akerr_ErrorContext akerr_last_ignored;
-```
-
-`static` means one per translation unit, and `AKERR_THREAD_LOCAL` means each one is
-thread-local. `sizeof(akerr_ErrorContext)` is **37,296 bytes**, so:
-
-| Build | TLS segment of `build/basic` |
-|---|---|
-| libakerror 2.0.1 | none at all |
-| libakerror 2.0.2 | 1,417,248 bytes — **1.35 MiB**, per thread |
-
-38 copies × 37,296 accounts for the segment exactly; `readelf -sW build/basic` shows all 38.
-It scales with translation-unit count, not with anything about the program, and every thread
-a host game spawns pays it again — which is worth knowing in a tree that spent a release
-taking `akbasic_Runtime` from 10.75 MiB to 2.40 MiB.
-
-It also emits **84 `-Wunused-variable` warnings**, one per TU that includes `akerror.h`
-without using `IGNORE`. Nothing here builds with `-Werror`, so it is noise rather than a
-failure — but a consumer that does cannot include the header.
-
-**Both are `libakerror` issue #37 and neither is worked around here**, per the rule above: a
-one-line `extern` in the header and a definition in `src/error.c` fixes it upstream, and
-patching our copy would fork the submodule. Delete this subsection when it lands.
+`IGNORE` still takes a *copy* of the ignored context so the pool slot can be released, which
+fixes a real leak, but the copy no longer costs TLS per translation unit. It was a file-scope
+`static` in the public header — one copy per TU, 37,296 bytes each, 1.35 MiB of thread-local
+storage in `build/basic` alone, plus 84 `-Wunused-variable` warnings for every TU that never
+called `IGNORE`. `libakerror` issue #37 moved it to an `extern` declaration in the header with
+a single definition in `src/error.c`, which restores one copy per thread and silences the
+warning. Issue #37 is closed and this subsection is gone accordingly.
 
 For both 0.x libraries the soname carries `MAJOR.MINOR` deliberately: 0.1 and 0.2 are
 *different* ABIs, and both become major-only at 1.0. Do not read `0.1 → 0.2` as a compatible