Replaced rattr.u.etc with rattr relevant types

This does a couple things:

- Makes attr-lists a bit more self-documenting.

- Adds a bit more type-safety. The LFSR_RATTR_* macros should be able to
  reject types that don't match the expected encoding.

- Makes it easier to adjust dsize estimates at one location.

  Specifically, this makes it harder to forget bptr's LFSR_BPTR_DSIZE.

---

Surprisingly this did have a small impact on code size. I'm not entirely
sure why, but considering how much of the codebase this touches I'm just
going to chalk this up to compiler noise:

           code          stack          ctx
  before: 35488           2440          636
  after:  35536 (+0.1%)   2440 (+0.0%)  636 (+0.0%)

lfsr_file_carve seems the hardest hit:

  function (0 added, 0 removed)      osize    nsize    dsize
  lfsr_file_open                        16       20       +4 (+25.0%)
  lfsr_file_carve                     1316     1356      +40 (+3.0%)
  lfsr_remove                          408      412       +4 (+1.0%)
  TOTAL                              35488    35536      +48 (+0.1%)

tests/test_files.toml

@@ -979,8 +979,7 @@ code = '''
     // delete any bshrub/btree
     lfsr_mdir_commit(&lfs, &file.b.o.mdir, LFSR_RATTRS(
             LFSR_RATTR(
-                LFSR_TAG_RM | LFSR_TAG_SUB | LFSR_TAG_STRUCT, 0,
-                NULL, 0))) => 0;
+                LFSR_TAG_RM | LFSR_TAG_SUB | LFSR_TAG_STRUCT, 0))) => 0;
 
     lfsr_file_close(&lfs, &file) => 0;
 
@@ -1095,27 +1094,25 @@ code = '''
 
     // create an empty bshrub
     lfsr_mdir_commit(&lfs, &file.b.o.mdir, LFSR_RATTRS(
-            LFSR_RATTR(
-                LFSR_TAG_SHRUBCOMMIT, 0,
+            LFSR_RATTR_SHRUBCOMMIT(
                 (&(lfsr_shrubcommit_t){
                     .bshrub=&file.b,
                     .rid=0,
                     .rattrs=((lfsr_rattr_t[]){
                         LFSR_RATTR_BUF(LFSR_TAG_DATA, +1, "?", 1)}),
-                    .rattr_count=1}), 0))) => 0;
+                    .rattr_count=1})))) => 0;
     lfsr_mdir_commit(&lfs, &file.b.o.mdir, LFSR_RATTRS(
-            LFSR_RATTR(
-                LFSR_TAG_SHRUBCOMMIT, 0,
+            LFSR_RATTR_SHRUBCOMMIT(
                 (&(lfsr_shrubcommit_t){
                     .bshrub=&file.b,
                     .rid=0,
                     .rattrs=((lfsr_rattr_t[]){
-                        LFSR_RATTR(LFSR_TAG_RM, -1, NULL, 0)}),
-                    .rattr_count=1}), 0))) => 0;
+                        LFSR_RATTR(LFSR_TAG_RM, -1)}),
+                    .rattr_count=1})))) => 0;
     lfsr_mdir_commit(&lfs, &file.b.o.mdir, LFSR_RATTRS(
-            LFSR_RATTR(
+            LFSR_RATTR_SHRUB(
                 LFSR_TAG_SUB | LFSR_TAG_BSHRUB, 0,
-                &file.b.shrub_, LFSR_SHRUB_DSIZE))) => 0;
+                &file.b.shrub_))) => 0;
 
     lfsr_file_close(&lfs, &file) => 0;
 
@@ -1234,11 +1231,11 @@ code = '''
     lfsr_rbyd_commit(&lfs, &file.b.shrub, 0, LFSR_RATTRS(
             LFSR_RATTR_BUF(LFSR_TAG_DATA, +1, "?", 1))) => 0;
     lfsr_rbyd_commit(&lfs, &file.b.shrub, 0, LFSR_RATTRS(
-            LFSR_RATTR(LFSR_TAG_RM, -1, NULL, 0))) => 0;
+            LFSR_RATTR(LFSR_TAG_RM, -1))) => 0;
     lfsr_mdir_commit(&lfs, &file.b.o.mdir, LFSR_RATTRS(
-            LFSR_RATTR(
+            LFSR_RATTR_BTREE(
                 LFSR_TAG_SUB | LFSR_TAG_BTREE, 0,
-                &file.b.shrub, LFSR_BTREE_DSIZE))) => 0;
+                &file.b.shrub))) => 0;
 
     lfsr_file_close(&lfs, &file) => 0;