* Reimplement r_buf_fread/fwrite
* Add slice buffer and introduce readonly field
* Do nothing if size is 0
* Prevents an overflow when 8 is subtracted from size.
* Fix ragg2 when patching outside currently existing buffer
* Implement r_mem_mmap_resize for systems where mremap is not defined
* r_buf_buffer can be called with no size arg as well
* Use size_t instead of ut64
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