Closes #2253

(cherry picked from commit cb8247e)

# Conflicts:
#	pkg/namespace/consts.go
#	pkg/namespace/namespace.go
#	pkg/namespace/namespace_test.go
#	pkg/shares/padding.go
#	specs/src/specs/namespace.md

This reverts commit 25b2df7.

Closes #2143

De-duplicate `ValidateBlobNamespace` and export it from `x/blob/types`
package. The namespace package needs to define its own `isBlobNamespace`
because it can't import `ValidateBlobNamespace` from `x/blob/types` as
that would introduce a circular dependency.

…to IsReserved function (#2194)

Closes ##2138
This PR also addresses the concerns raised in the
[comment](#2138 (comment))
by introducing a distinction between two types of reserved namespaces.
Namespaces within the range [0-255] are now identified as "Primary
Reserved Namespaces," while any other reserved namespaces beyond this
range are categorized as "Non-Primary Reserved Namespaces." Hopefully,
this differentiation provides better clarity and organization regarding
namespace allocation and usage within the code.

- [x] New and updated code has appropriate documentation
- [x] New and updated code has new and/or updated testing
- [x] Required CI checks are passing
- [x] Visual proof for any user facing features like CLI or
documentation updates
- [x] Linked issues closed with keywords

Closes #2142

Closes #2253