`provekit/prover/src/witness/mod`: Use better entropy source and proper sampling.

[recmo]

On 2025-08-29 in 2a57572 “Merge pull request #153 from worldfnd/px/refactor”:

Use better entropy source and proper sampling.

pub(crate) mod witness_io_pattern;

/// Complete a partial witness with random values.
#[instrument(skip_all, fields(size = witness.len()))]
pub(crate) fn fill_witness(witness: Vec<Option<FieldElement>>) -> Result<Vec<FieldElement>> {
    // TODO: Use better entropy source and proper sampling.
    let mut rng = rng();
    let mut count = 0;
    let witness = witness
        .iter()
        .map(|f| {

From provekit/prover/src/witness/mod.rs:16