feat(nx-object): read a KIP1 and a CNMT, and expand packed segments

[LNSD]

Completes the read side for the formats the crate already builds. Expanding a segment stays a separate call rather than an accessor: a reader borrows its buffer and has nowhere to put the result, so the allocation and the failure are both the caller's to see.

• Add blz::decompress, taking the expanded length as an argument because a stored stream is padded to four bytes and records no length of its own
• Add read::kip, proving each segment's stored bytes lie inside the image and expanding the three the header marks packed; bss reads as an empty slice, since it occupies no bytes in the file
• Add read::cnmt, exposing the content records and leaving an extended header unread when the meta type is not one this crate models, rather than reinterpreting it as the wrong structure
• Add Nso::text, Nso::rodata, and Nso::data, returning the segment as the loader maps it — page padding included, because the recorded size and hash both cover it
• Fix two compress defects the new round-trip sweep found: a layout saving less than the trailer underflowed extra_len and panicked, and one saving exactly the trailer wrote a zero there, which is the marker for a stored stream and decoded as the wrong form