Merge upstream/ripple/smart-escrow into xrplf/smart-contracts

Upstream rewrote the wasm VM and host-function system (Rust `crates/`
bridged via cxx), collapsed `transactions.macro` onto `TxSettings`, and
moved invariant running from `ApplyContext` to `Transactor`. This merge
resolves those conflicts and the breaks that carried no conflict marker.

Conflict resolutions of note:
- transactions.macro: took upstream's 5-argument `TxSettings` form and
  re-expressed our `emitable` column as `TxSettings::emittance`, a new
  scoped `Emittance` enum in TxSettings.h. `Emitable.cpp` and the
  transaction code generator read the new member.
- sfields.macro: upstream claimed UINT32 75-80, so `sfParameterFlag`
  moves from 80 to 86. The amendment is not live, so no wire break.
- HostFunc.h: took upstream's version, which drops `floatRoot`, and
  re-added the 15 contract virtuals. `setDataNestedObjectField`'s
  parameters are renamed to `(account, key, nestedKey, value)` to match
  the implementation; the wire order is unchanged.
- WasmCommon.h: `SubmitTxnFailure` (-21) and `InvalidState` (-22) join
  upstream's enum and the Rust `host_errors!` table. `Success` is gone;
  the helpers that compared against it now return `expected<void, ...>`.
- Transactor.cpp: kept the emitted-transaction pass, now using
  `checkInvariants(result, fee, InvariantScope::ProtocolOnly)`.

Breaks with no conflict marker:
- `Emitable.cpp` used the 8-argument TRANSACTION macro.
- `STTx::getSeqValue` is gone; use `getSeqProxy().value()`.
- `NetworkOPsImp::subLock_` is now `streamLock_`, held with `scoped_lock`.
- The `LedgerEntryHelpers` namespace is now `ledger_entry_helpers`.
- `keylet::vault` takes a `SeqProxy`. The three contract `ledger_entry`
  parsers were copy-pasted from the vault one and returned vault keylets;
  they now build contract, contract source and contract data keylets from
  their own fields. `contract_hash` is added to jss.

The 15 contract host functions still register through the deleted C++
wrapper layer, so contract bytecode does not run yet. Porting them to the
Rust-declared ABI is the next commit.

include/xrpl/protocol/STObject.h

@@ -444,8 +444,6 @@ public:
 
     bool
     operator==(STObject const& o) const;
-    bool
-    operator!=(STObject const& o) const;
 
     class FieldErr;
 
@@ -679,36 +677,6 @@ public:
         return !lhs.engaged() || *lhs == *rhs;
     }
 
-    friend bool
-    operator!=(OptionalProxy const& lhs, std::nullopt_t) noexcept
-    {
-        return !(lhs == std::nullopt);
-    }
-
-    friend bool
-    operator!=(std::nullopt_t, OptionalProxy const& rhs) noexcept
-    {
-        return !(rhs == std::nullopt);
-    }
-
-    friend bool
-    operator!=(OptionalProxy const& lhs, optional_type const& rhs) noexcept
-    {
-        return !(lhs == rhs);
-    }
-
-    friend bool
-    operator!=(optional_type const& lhs, OptionalProxy const& rhs) noexcept
-    {
-        return !(lhs == rhs);
-    }
-
-    friend bool
-    operator!=(OptionalProxy const& lhs, OptionalProxy const& rhs) noexcept
-    {
-        return !(lhs == rhs);
-    }
-
     // Emulate std::optional::value_or
     [[nodiscard]] value_type
     valueOr(value_type val) const;
@@ -1214,12 +1182,6 @@ STObject::setFieldH160(SField const& field, BaseUInt<160, Tag> const& v)
     }
 }
 
-inline bool
-STObject::operator!=(STObject const& o) const
-{
-    return !(*this == o);
-}
-
 template <typename T, typename V>
 V
 STObject::getFieldByValue(SField const& field) const