chore!: consistent share prefix for tail padding

[rootulp]

Closes #1350

After updating tail padding to have the same share prefix as namespace padding, I realized it was possible to make a few refactors so that all padding is consistent with respect to naming and tests:

1. Move all 3 types of padding to padding.go
2. Rename "namespaced padded" => "namespace padding" to conform to "tail padding"
3. Rename ReservedNamespacePadding => ReservedPaddingNamespaceID to conform to the other appconsts that are namespace IDs
4. Define a share.IsPadding method

[rootulp]

[for reviewers] this hash had to be updated because the schema for tail padding shares is now different which results in a completely different hash.

[codecov-commenter]

Codecov Report

Merging #1353 (dd0e5f4) into main (990c720) will decrease coverage by 0.04%.
The diff coverage is 92.64%.

@@            Coverage Diff             @@
##             main    #1353      +/-   ##
==========================================
- Coverage   48.31%   48.28%   -0.04%     
==========================================
  Files          79       78       -1     
  Lines        4425     4422       -3     
==========================================
- Hits         2138     2135       -3     
  Misses       2107     2107              
  Partials      180      180              

Impacted Files	Coverage Δ
pkg/shares/shares.go	87.50% <90.90%> (-0.66%)	⬇️
pkg/shares/padding.go	93.10% <93.10%> (ø)
pkg/da/data_availability_header.go	78.50% <100.00%> (-1.15%)	⬇️
pkg/shares/parse_sparse_shares.go	64.40% <100.00%> (ø)
pkg/shares/share_splitting.go	75.78% <100.00%> (ø)
pkg/shares/split_sparse_shares.go	65.16% <100.00%> (ø)

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[evan-forbes]

nice refactor, it is much appreciated