Consume libakgl 0.2.0 and libakstdlib 0.2.0

Rebasing the defect filing onto libakgl's origin/main brought two upstream
commits with it -- "Consume libakstdlib 0.2.0" and "Bump libakgl to 0.2.0" --
and libakgl's sources now use the 0.2.0 akstdlib API. Our CMakeLists declares
akstdlib::akstdlib from our own tree first, so libakgl was compiling 0.2.0-era
code against 0.1.0 headers and failing on aksl_fwrite, aksl_fread and
aksl_realpath. The two have to move together.

The code change is one call site. aksl_fwrite now takes a required size_t
*nmemb_out and reports a short transfer as AKERR_IO rather than a silent
success, so DSAVE onto a full disk is an error a program sees where before it
reported nothing. The count is passed and discarded on purpose: the library does
the noticing now.

The documentation change is larger, because libakstdlib 0.2.0 fixed all six of
the confirmed defects TODO.md section 1.9 was built around. That section was a
table of bans; leaving it would send an agent around a workaround for functions
that now work. The aksl_ato* family raises AKERR_VALUE on no digits or trailing
junk and ERANGE on overflow -- exactly the contract that section demanded --
aksl_list_append no longer truncates, aksl_list_iterate no longer skips the
first half, AKERR_ITERATOR_BREAK stops a tree traversal, and aksl_realpath no
longer reads uninitialised memory. One caveat survives: aksl_strhash_djb2 still
sign-extends char, which section 1.3 already covers and the symbol tables still
cannot reach.

src/convert.c has therefore outlived its reason, and is deliberately left in
place. Its own note said to delete it when libakstdlib grew the contract, and
that condition is now met -- but doing it touches four call sites, changes the
raised status from AKBASIC_ERR_VALUE to AKERR_VALUE where section 1.8 says
message text is part of the acceptance contract, and would silently gut the CI
mutation job, which is bounded to src/convert.c and src/symtab.c. Section 1.9
now lists all of that. Worth doing on purpose rather than as a side effect of a
version bump.

libakgl defect #14 is closed by its own 1066ac7, which bumped it to 0.2.0 while
this was being written. The requirement is no longer pinned by submodule commit
in the README, because AKGL_VERSION_AT_LEAST(0, 2, 0) finally means something.

70/70 core, 71/71 with libakgl, 70/70 under ASan+UBSan, clean under
-Wall -Wextra, doxygen clean.

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

src/runtime_commands.c

@@ -525,6 +525,7 @@ akerr_ErrorContext *akbasic_cmd_dsave(akbasic_Runtime *obj, akbasic_ASTLeaf *exp
     FILE *fp = NULL;
     int64_t i = 0;
     int count = 0;
+    size_t written = 0;
 
     (void)lval; (void)rval;
     PASS(errctx, filename_argument(obj, expr, filename, sizeof(filename)));
@@ -536,7 +537,14 @@ akerr_ErrorContext *akbasic_cmd_dsave(akbasic_Runtime *obj, akbasic_ASTLeaf *exp
 		continue;
 	    }
 	    snprintf(line, sizeof(line), "%" PRId64 " %s\n", i, obj->source[i].code);
-	    PASS(errctx, aksl_fwrite(line, 1, strlen(line), fp));
+	    /*
+	     * The written count is required by libakstdlib 0.2.0 and discarded
+	     * here on purpose: a short write is no longer something a caller has
+	     * to notice for itself, because that release made it an AKERR_IO
+	     * rather than a silent success. Before it, a DSAVE onto a full disk
+	     * reported nothing.
+	     */
+	    PASS(errctx, aksl_fwrite(line, 1, strlen(line), fp, &written));
 	    count += 1;
 	}
     } CLEANUP {