Cardano Updates

The infallible From<Vec<i128>> was a footgun: 15.0.3 built malformed
Int silently for out-of-range values; the interim 16.0.0 work
tightened that to a panic. Both are wrong at a public boundary, so
replace with TryFrom<Vec<i128>> returning JsError on overflow.
Internal call sites (tx_builder_constants, fakes, tests) use
.try_from(...).unwrap() since their values are compile-time known
to fit. Tests assert the error path; the panic test is gone.

bigint_as_int_handles_min_i128 already exercises the new
(Sign::Minus, [0, 1]) arm. bigint_as_int_branch_coverage now
explicitly walks the remaining match arms — zero, single-limb
positive and negative across the full u64 range, and multi-limb
inputs that must return None on both sides of the bound.

Conway CDDL constrains mint amounts to
  mint = {+ policy_id => {+ asset_name => nonzero_int64}}
i.e. each amount must be a non-zero int64. Previously MintAssets::insert
only rejected zero; values up to the full CBOR int range were accepted,
producing on-chain-invalid mints that would also fail later in MultiAsset
conversion (BigNum/u64).

* MintAssets::insert and MintAssets::new_from_entry now reject any value
  whose magnitude exceeds i64::MAX with a clear CDDL-citing error.
* Int gains a pub(crate) fits_int64() helper for shared use.
* CBOR deserialization is intentionally left permissive: it preserves
  on-the-wire values so callers can inspect or apply their own policy.
  Validation lives at the construction boundary instead, which is the
  only path that goes through MintAssets::insert.
* Tests updated: cover the lower CBOR-int corner, the int64 boundary
  edges on both sides, and the deserialize-passthrough behavior.

lib.rs falls back to noop_proc_macro::wasm_bindgen both for non-wasm
builds and for wasm builds that opt out of wasm-bindgen via the
`dont-expose-wasm` feature. The crate was previously declared only
in the non-wasm target dependency table, so consumers depending on
csl with `features = ["dont-expose-wasm"]` and target=wasm32 hit
`unresolved import `noop_proc_macro``. Declare it as an optional
wasm-target dep and wire `dont-expose-wasm` to activate it via
`dep:noop_proc_macro` — keeps it out of normal wasm builds.

asm.js needs wasm-bindgen <=0.2.93 (binaryen's wasm2js rejects
the multi-table modules emitted from 0.2.95 onward; 0.2.94 is
yanked, 0.2.96+ requires nightly Rust). Other targets use
0.2.103, which is the floor the manifest now permits.

The manifest opens the range to ">=0.2.93, <0.3" and the build
helper drives the precise pick via `cargo update --precise` per
variant. Cargo.lock is not checked in, so the pin lives only in
the local lock for the duration of the build.

Pin the wire format with byte-exact vectors for canonical major-0
and major-1 across all header-size boundaries (1/2/3/5/9 bytes).
Covers RFC 8949 Appendix A examples plus the i64::MIN and -2^64
edges that distinguish Cardano's CBOR int from a plain i64. Adds
decode-vector and non-int-type rejection tests.

2.4.0 adds write_negative_integer_sz / Sz which natively handle i128
nint payloads up to u64::MAX. Replace the hand-rolled canonical
nint encoder with the upstream helper.

JsError has no Display impl on wasm targets, so format! "{}" fails
to compile. Switch to "{:?}" — matches Int::from_str.

The bounds describe the CBOR int domain, not the storage type. Drop
the i128 suffix and use CBOR_MIN/CBOR_MAX so the intent is explicit
at call sites.

- MintAssets::insert and CBOR deserializer reject Int::MIN_I128
  (-2^64), since |x| = 2^64 cannot fit a u64 burn amount in
  MultiAsset; previously Mint::as_negative_multiasset() would panic.
- Mint::as_multiasset replaces .unwrap() with if-let as
  defense-in-depth.
- BigInt::as_int recognizes the two-limb [0, 1] representation of
  -2^64 and maps it to Int::MIN_I128 instead of returning None.
- Tests: MintAssets rejection (insert and CBOR), BigInt::as_int
  round-trip across the full CBOR int range.

Validate Int construction against CBOR int bounds, fix nint
serialization for values below i64::MIN, and add checked/
saturating arithmetic helpers. Adds boundary tests covering
TryFrom, FromStr, CBOR roundtrip, and CostModel::from.