Extended lfsr_format with some gc flags

These fall out quite naturally when you consider that we call
lfsr_mountinited internally to check that our format was successful.

That being said... they don't really do anything right now since we only
write a single mdir:

- LFS_F_COMPACT - The only gc operation that _might_ actually do
  something is LFS_F_COMPACT, but only if our fs config exceeds >1/2 the
  block size. But I'm not sure littlefs will even be able to write file
  metadata if this happens...

- LFS_F_CKMETA - We already check the only mdir by calling
  lfsr_mountinited, which implicitly fetches the mrootanchor.

- LFS_F_CKDATA - We uh, don't have any data immediately after
  lfsr_format. But I guess it doesn't hurt to keep this around for
  consistency, it at least implies CKMETA.

Hopefully these flags will be more interesting if/when we start adding
auxiliary trees to the filesystem, otherwise they may be worth reverting
in the future...

Until then, they at least provide some consistency, and I guess a way to
triply check that format was successful.

---

This could probably be better deduplicated, but calling lfsr_fs_gc from
both lfsr_mount and lfsr_format provides a bit better code organization:

           code          stack
  before: 36448           2680
  after:  36480 (+0.1%)   2680 (+0.0%)

tests/test_mount.toml

@@ -11,14 +11,28 @@ code = '''
     lfsr_unmount(&lfs) => 0;
 '''
 
-# test that various mount flags are returned by lfsr_fs_stat
+# test that various mount flags don't assert and are returned by
+# lfsr_fs_stat
 [cases.test_mount_flags]
 defines.RDONLY = [false, true]
 defines.CKPROGS = [false, true]
 defines.CKREADS = [false, true]
 defines.FLUSH = [false, true]
 defines.SYNC = [false, true]
-if = 'LFS_IFDEF_CKREADS(true, !CKREADS)'
+defines.MTREEONLY = [false, true]
+defines.MKCONSISTENT = [false, true]
+defines.LOOKAHEAD = [false, true]
+defines.COMPACT = [false, true]
+defines.CKMETA = [false, true]
+defines.CKDATA = [false, true]
+if = [
+    'LFS_IFDEF_CKREADS(true, !CKREADS)',
+    '!RDONLY || !MKCONSISTENT',
+    '!RDONLY || !LOOKAHEAD',
+    '!RDONLY || !COMPACT',
+    '!MTREEONLY || !LOOKAHEAD',
+    '!MTREEONLY || !CKDATA',
+]
 code = '''
     lfs_t lfs;
     lfsr_format(&lfs, LFS_F_RDWR, CFG) => 0;
@@ -27,9 +41,16 @@ code = '''
                 | ((CKPROGS) ? LFS_M_CKPROGS : 0)
                 | ((CKREADS) ? LFS_IFDEF_CKREADS(LFS_M_CKREADS, 0) : 0)
                 | ((FLUSH) ? LFS_M_FLUSH : 0)
-                | ((SYNC) ? LFS_M_SYNC : 0),
+                | ((SYNC) ? LFS_M_SYNC : 0)
+                | ((MTREEONLY) ? LFS_M_MTREEONLY : 0)
+                | ((MKCONSISTENT) ? LFS_M_MKCONSISTENT : 0)
+                | ((LOOKAHEAD) ? LFS_M_LOOKAHEAD : 0)
+                | ((COMPACT) ? LFS_M_COMPACT : 0)
+                | ((CKMETA) ? LFS_M_CKMETA : 0)
+                | ((CKDATA) ? LFS_M_CKDATA : 0),
             CFG) => 0;
 
+    // lfsr_fs_stat only returns some flags
     struct lfs_fsinfo fsinfo;
     lfsr_fs_stat(&lfs, &fsinfo) => 0;
     assert(fsinfo.flags == (
@@ -38,8 +59,8 @@ code = '''
                 | ((CKREADS) ? LFS_IFDEF_CKREADS(LFS_I_CKREADS, 0) : 0)
                 | ((FLUSH) ? LFS_I_FLUSH : 0)
                 | ((SYNC) ? LFS_I_SYNC : 0)
-                | LFS_I_CANLOOKAHEAD
-                | LFS_I_UNCOMPACTED));
+                | ((!LOOKAHEAD) ? LFS_I_CANLOOKAHEAD : 0)
+                | ((!COMPACT) ? LFS_I_UNCOMPACTED : 0)));
 
     lfsr_unmount(&lfs) => 0;
 '''
@@ -50,13 +71,24 @@ code = '''
 [cases.test_mount_format_flags]
 defines.CKPROGS = [false, true]
 defines.CKREADS = [false, true]
-if = 'LFS_IFDEF_CKREADS(true, !CKREADS)'
+defines.MTREEONLY = [false, true]
+defines.COMPACT = [false, true]
+defines.CKMETA = [false, true]
+defines.CKDATA = [false, true]
+if = [
+    'LFS_IFDEF_CKREADS(true, !CKREADS)',
+    '!MTREEONLY || !CKDATA',
+]
 code = '''
     lfs_t lfs;
     lfsr_format(&lfs,
             LFS_F_RDWR
                 | ((CKPROGS) ? LFS_F_CKPROGS : 0)
-                | ((CKREADS) ? LFS_IFDEF_CKREADS(LFS_F_CKREADS, 0) : 0),
+                | ((CKREADS) ? LFS_IFDEF_CKREADS(LFS_F_CKREADS, 0) : 0)
+                | ((MTREEONLY) ? LFS_M_MTREEONLY : 0)
+                | ((COMPACT) ? LFS_M_COMPACT : 0)
+                | ((CKMETA) ? LFS_M_CKMETA : 0)
+                | ((CKDATA) ? LFS_M_CKDATA : 0),
             CFG) => 0;
 
     lfsr_mount(&lfs, LFS_M_RDWR, CFG) => 0;