Cardano Updates

Rewrites `PlutusLedgerApi.V1.Data.Value.valueOf` so the non-builtin lookup
path walks the underlying `BuiltinList` directly via `unsafeDataAsMap` /
`unsafeDataAsB` / `unsafeDataAsI`, compares keys with `equalsByteString`,
and short-circuits on the first match. No `Maybe` is materialised: the
"absent" answer is `0`, returned in-place by the `nilCase` of each
traversal. Avoids `withCurrencySymbol`'s continuation + `Map.lookup`'s
`Maybe`-wrapping, and bypasses the `ToData k`/`UnsafeFromData a` dictionary
work that `AssocMap.lookup` does per element. Semantics preserved.

Adds `Spec.Data.Value.test_valueOf`: a QuickCheck property that compiles
`valueOf` via TH, evaluates it on the CEK machine, and compares the result
against the host-Haskell `valueOf` for the same inputs. Differential test
against the Plinth compiler — any divergence is a compilation bug, not a
semantics bug.

Budget evidence (lookup matrix, `unsafeDataAsValue` baseline) lives on the
companion experimental branch `yura/issue-2242-valueof-evidence`, kept out
of this PR to avoid carrying ~96 golden files that would only ever regenerate
on upstream plugin/cost-model changes.

For IntersectMBO/plutus-private#2242.

Prevent the secret scalar from leaking through `{:?}` on the key or any type that embeds it (signer, signing-key bundle).

Make `BaseFieldElement::from_raw` public so out-of-circuit SNARK signers can
reduce a SHA-256 digest into the same field element the IVC genesis-signature
gadget consumes as witness.