fix(eth2util): sort deposit-data listing, seed keystore uuids from rng

[iamquang95]

Fix #627

• Sort the deposit-data file listing. read_dir order is filesystem-dependent, so an index could mean a different amount on another machine. Matches charon's sorted glob.
• Draw keystore uuids from the rng parameter instead of Uuid::new_v4(), which silently bypassed it. Seeded keystores are now reproducible.
• Deliberate deviations from charon (comments explain local rationale only): strict withdrawal_credentials length check, zero-sig before domain resolution, SSE slot saturation, exit fork version from the BN spec, v4 bits on keystore uuids, escaped . in the keystore regex.