wasm: refuse unknown fields on every Arca object

[GracedEternalKingCabbageMan]

serde_wasm_bindgen reads a struct by asking the JavaScript object for each field the struct names. A field the struct does not name is therefore never seen, and deny_unknown_fields has nothing to refuse. Before this change:

• new ArkVerifier(network, { operator, maxExitDelaySecond: 172800 }) was accepted, and the bound took its default. The new test fails with Missing expected exception.
• signCsfs(..., { maxUncomitted: '9999000' }) ignored the misspelt field, so the ceiling fell back to 0. The signer refused for that reason instead: the committed outputs leave 9999000 atoms ... the ceiling is 0.

Every Arca object is now read whole first, with all of its keys, and only then converted into its type, where deny_unknown_fields applies at every level. That covers the policy and its fee-rate floor, the limits, the message, and the message's source, outputs and inputs. A source is read as a record or in the named form depending on whether it has record, so a stray field is named in the refusal instead of being reported as matching no variant.

Tested, wasm --dev --target nodejs:

• ark_records.js refuses unknown field \maxExitDelaySecond`and, insideminReserveFeeRate, unknown field `mutliple``.
• arca_signers.js refuses maxUncomitted in the limits, salts in a named source, leafId beside record, amount in an output, vout in an input, tme in an unroll and connectorAsset in a release.
• The rest of both suites still passes.
• ark_regtest (5 leaves accepted, 25 refused) and the signers' arca_regtest.py (Tests successful), whose objects all cross this boundary, pass.