`CCtx::init_using_cdict` and `DCtx::init_using_ddict` (`experimental`
feature, deprecated) took the dictionary as `&CDict<'b>` and `&DDict<'b>`
with only `'b: 'a`, so the dictionary itself could be dropped while the
context still pointed at it. The same mistake in other constructors was
fixed earlier (<https://github.com/gyscos/zstd-rs/issues/365>).
The flaw was corrected by taking `&'a CDict<'b>` and `&'a DDict<'b>`.