Take libakgl 0.7.0, and refuse an over-long type or field name

0.6.0 and 0.7.0 break nothing here: 0.6.0 is three arcade-physics fixes and a
physics.max_timestep property this port does not use, and 0.7.0 reports failures
libakstdlib's wrappers were already catching and takes libakerror 2.0.1 so it
can drop the exit-status trap its own suites needed. That is the same defect
include/akbasic/error.h guards for this band, now fixed at the source rather
than worked around in two places.

The floor moves to 0.7.0 anyway. The soname carries MAJOR.MINOR while the major
is 0, so deciding for ourselves which of libakgl's minor releases were really
compatible is exactly the judgement it exists to take away.

0.7.0 is largely about a defect class worth checking for here rather than
assuming past: ten unterminated strncpy calls into fixed-width name fields. Ours
are clean -- every one is bounded to size - 1 and every buffer is either
explicitly terminated afterwards or memset first, checked site by site. But two
of them, both written last week in src/structtype.c, truncated an over-long name
silently, and truncation is an error everywhere else in this interpreter. It
matters more for a name than for a value: two long type names trimmed to the
same 31 characters collide, and the second is then reported as redeclaring a
type the program never wrote.

Both are refused now, showing the name as written. The check was unreachable as
first drafted, because the prescan read words into a buffer the size of the
limit and so trimmed them before anything could look -- the scratch is twice the
limit now, which is what makes the two cases distinguishable at all.
tests/struct_types.c pins that it stays reachable.

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

README.md

@@ -144,7 +144,7 @@ nothing to install first.
 * [libakstdlib](https://source.starfort.tech/andrew/libakstdlib) 0.2.0 — libc wrappers that
   report through `libakerror`. String-to-number conversion goes straight to it, which is why
   `VAL("garbage")` is an error rather than a silent `0`.
-* [libakgl](https://source.starfort.tech/andrew/libakgl) 0.5.0 — **optional**, only for
+* [libakgl](https://source.starfort.tech/andrew/libakgl) 0.7.0 — **optional**, only for
   `-DAKBASIC_WITH_AKGL=ON`. Pulls in SDL3. Its soname carries `MAJOR.MINOR` while the major is 0,
   so rebuild rather than relink.
 * [basicinterpret](https://source.starfort.tech/andrew/basicinterpret) — the Go original.