Added some metadata_max testing

- Added METADATA_MAX to test_runner.
- Added METADATA_MAX to bench_runner.
- Added a simple metadata_max test to test_superblocks, for lack of
  better location.

There have been several issues floating around related to metadata_max
and LFS_ERR_NOSPC which makes me think there's a bug in our metadata_max
logic.

metadata_max was a quick patch and is relatively untested, so an
undetected bug isn't too surprising. This commit adds at least some
testing over metadata_max.

Sure enough, the new test_superblocks_metadata_max test reveals a
curious LFS_ERR_NAMETOOLONG error that shouldn't be there.

More investigation needed.

tests/test_superblocks.toml

@@ -523,3 +523,30 @@ code = '''
     assert(memcmp(buffer, "hello!", 6) == 0);
     lfs_unmount(&lfs) => 0;
 '''
+
+# test that metadata_max does not cause problems for superblock compaction
+[cases.test_superblocks_metadata_max]
+defines.METADATA_MAX = [
+    'lfs_max(512, PROG_SIZE)',
+    'lfs_max(BLOCK_SIZE/2, PROG_SIZE)',
+    'BLOCK_SIZE'
+]
+defines.N = [10, 100, 1000]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+    lfs_mount(&lfs, cfg) => 0;
+    for (int i = 0; i < N; i++) {
+        lfs_file_t file;
+        char name[256];
+        sprintf(name, "hello%03x", i);
+        lfs_file_open(&lfs, &file, name,
+                LFS_O_WRONLY | LFS_O_CREAT | LFS_O_EXCL) => 0;
+        lfs_file_close(&lfs, &file) => 0;
+        struct lfs_info info;
+        lfs_stat(&lfs, name, &info) => 0;
+        assert(strcmp(info.name, name) == 0);
+        assert(info.type == LFS_TYPE_REG);
+    }
+    lfs_unmount(&lfs) => 0;
+'''