Consider storing SRS in uncompressed form

[davxy]

SRS (aka chunks here) is currently stored in compressed form!
Consider trading space (2x) for speed (~3x)

Storing SRS items uncompressed (96 bytes instead of 48) eliminates the point decompression cost (field square root) on every fetch_srs_range call.

The accumulate operations (push of new members during ring commitment construction), which are the main consumers of SRS reads, show a ~3x speedup (e.g. for 50 new members: 18.95 ms -> 6.44 ms).

Verify and IETF operations are unaffected (no SRS reads).

See davxy/ark-substrate-examples#4 diff for comparisons

cc @georgepisaltu @ggwpez