Version at 0.2.0: complete the wishlist, document it, gate the docs

Closes what was left of TODO.md sections 1, 2 and 3, and rewrites that
file to hold outstanding items only.

The API break gets a minor bump, because pre-1.0 the soname carries
MAJOR.MINOR and 0.1 and 0.2 are therefore different ABIs. Five
signatures changed and the ato* contract with them; UPGRADING.md is new
and lists every one, with the before/after for the cases the compiler
cannot warn about.

Section 3.1 is finished: reallocarray with the multiplication checked,
aligned_alloc and posix_memalign, asprintf/vasprintf, scanf/vscanf.
Four functions on that list are deliberately absent rather than missing
-- sprintf, strtok, setbuf and perror -- and TODO.md now says which and
why, so nobody adds them thinking they were forgotten.

Section 1.9, the cross-cutting tests:

  tests/test_pool.c    drives every failure path AKERR_MAX_ARRAY_ERROR
                       + 10 times and checks the pool after each round,
                       because a wrapper that leaks a slot fails a
                       hundred calls later in unrelated code. It also
                       asserts that each error names the function and
                       file it was raised from, which is what catches a
                       FAIL that migrates into a helper during a
                       refactor: status right, message right, origin
                       quietly lying.
  tests/negative/      two sources that must FAIL to compile, built with
                       -Werror and registered WILL_FAIL. AKERR_NOIGNORE
                       and the format attributes are enforced by the
                       compiler and by nothing else; drop either and
                       every ordinary test still passes.

Thread safety is answered rather than tested: the library is not
thread-safe and cannot be made so from here, because libakerror's error
pool is an unlocked process-global array. README.md says so plainly and
TODO.md carries it as the item blocking any future pthread wrappers.

Doxygen is configured and gated. All 147 public functions have @brief,
a @param each, @throws per status and @return; EXTRACT_ALL is off and
WARN_NO_PARAMDOC on, so `cmake --build build --target docs` fails on an
undocumented entity. It ran to 0 warnings. The Doxyfile carries no
version -- cmake/RunDoxygen.cmake feeds PROJECT_NUMBER in from
project(), so that stays the one place a version is written.

CI now builds against the submodule it pins instead of also installing
libakerror@main and never linking it, adds -Werror, and gains a
sanitizer job. The pre-push hook matches, and runs the docs check too.

Coverage: 99.5% of lines (1643/1651), 100% of functions (147/147). The
eight uncovered lines are each uncovered on purpose and TODO.md says
which and why.

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

tests/test_strto.c

@@ -111,6 +111,53 @@ static int test_no_digits_is_an_error_even_with_an_endptr(void)
     return 0;
 }
 
+/*
+ * Every form writes through endptr, not just the two the other tests happen to
+ * use. Each type has its own function body, so "strtol handles endptr" says
+ * nothing whatsoever about strtoull.
+ */
+static int test_every_form_writes_the_endptr(void)
+{
+    const char *input = "42rest";
+    char *end = NULL;
+    long lout = 0;
+    long long llout = 0;
+    unsigned long ulout = 0;
+    unsigned long long ullout = 0;
+    double dout = 0.0;
+    float fout = 0.0f;
+    long double ldout = 0.0L;
+
+    end = NULL;
+    AKSL_CHECK_OK(aksl_strtol(input, &end, 10, &lout));
+    AKSL_CHECK(lout == 42 && strcmp(end, "rest") == 0);
+
+    end = NULL;
+    AKSL_CHECK_OK(aksl_strtoll(input, &end, 10, &llout));
+    AKSL_CHECK(llout == 42 && strcmp(end, "rest") == 0);
+
+    end = NULL;
+    AKSL_CHECK_OK(aksl_strtoul(input, &end, 10, &ulout));
+    AKSL_CHECK(ulout == 42 && strcmp(end, "rest") == 0);
+
+    end = NULL;
+    AKSL_CHECK_OK(aksl_strtoull(input, &end, 10, &ullout));
+    AKSL_CHECK(ullout == 42 && strcmp(end, "rest") == 0);
+
+    end = NULL;
+    AKSL_CHECK_OK(aksl_strtod(input, &end, &dout));
+    AKSL_CHECK(dout == 42.0 && strcmp(end, "rest") == 0);
+
+    end = NULL;
+    AKSL_CHECK_OK(aksl_strtof(input, &end, &fout));
+    AKSL_CHECK(fout == 42.0f && strcmp(end, "rest") == 0);
+
+    end = NULL;
+    AKSL_CHECK_OK(aksl_strtold(input, &end, &ldout));
+    AKSL_CHECK(ldout == 42.0L && strcmp(end, "rest") == 0);
+    return 0;
+}
+
 /* Successive calls chained through endptr walk a whole list of numbers. */
 static int test_endptr_chains_across_a_list(void)
 {
@@ -277,6 +324,7 @@ int main(void)
     AKSL_RUN(failures, test_invalid_base_is_rejected);
 
     AKSL_RUN(failures, test_endptr_reports_where_parsing_stopped);
+    AKSL_RUN(failures, test_every_form_writes_the_endptr);
     AKSL_RUN(failures, test_no_digits_is_an_error_even_with_an_endptr);
     AKSL_RUN(failures, test_endptr_chains_across_a_list);