[F34] mxaccess-asb: AddMonitoredItems body uses DataContract field names

Rewrite push_monitored_item_body to emit the DataContract field-suffix
names from AsbContracts.cs:940-965 (activeField, bufferedField,
itemField, sampleIntervalField, timeDeadbandField, userDataField,
valueDeadbandField) under prefix `b` bound to the
http://schemas.datacontract.org/2004/07/ArchestrAServices.ASBIDataV2Contract
namespace. The <Items> wrapper now declares xmlns:b + xmlns:i.

The legacy XmlSerializer property names (<Active>, <Item>,
<SampleInterval>, <Buffered>) only matter for the canonical-XML HMAC
signing input — that emitter at xml_canonical::emit_monitored_item is
unchanged and F28 fixture byte-equality still holds for all 13 ops.
On the binary NBFX wire MxDataProvider's DataContractSerializer
expects the field-suffix form.

Wire-byte type encoding matches the captured fixture
(add-monitored-items-request-wire.bin): bool → Bool record, ulong →
Zero/One/Chars (XmlConvert decimal text), ushort → Zero/One/Int8/Int16/Int32
(smallest-fit binary). Empty string? + null byte[]? emit as empty
elements with no <i:nil> attribute (matching the wire). Field order
follows the explicit [DataMember(Order = N)] sequence.

Adjacent: ItemIdentity is nested via DataContract field names too —
NOT the binary <ASBIData> fast-path, which only kicks in at top-level
message body members.

Verified live against AVEVA MxDataProvider: AddMonitoredItems now
returns 1 status item with error_code=0x0000 (previously 0 items;
the silent failure was the deliberate DC-schema mismatch); Publish
poll #4 delivers the actual tag value as
AsbVariant { type_id: 4, length: 4, payload: [99,0,0,0] } through the
F26 stream.

Pre-existing clippy::format_collect errors in auth.rs:339,342 and
client.rs:952 fixed in passing — they were blocking workspace clippy
otherwise.

Workspace: 757 → 758 tests, clippy -D warnings clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

rust/crates/mxaccess-asb-nettcp/src/auth.rs

@@ -335,11 +335,18 @@ impl AsbAuthenticator {
             out.as_mut_slice(),
         );
         if std::env::var("MX_ASB_TRACE_DERIVE").ok().is_some() {
+            use std::fmt::Write as _;
             eprintln!("asb.derive.crypto_key.len={}", crypto_key.len());
-            let hex: String = crypto_key.iter().map(|b| format!("{b:02X}")).collect();
+            let hex = crypto_key.iter().fold(String::new(), |mut s, b| {
+                let _ = write!(s, "{b:02X}");
+                s
+            });
             eprintln!("asb.derive.crypto_key.hex={hex}");
             eprintln!("asb.derive.crypto_key.b64={password_b64}");
-            let aes_hex: String = out.iter().map(|b| format!("{b:02X}")).collect();
+            let aes_hex = out.iter().fold(String::new(), |mut s, b| {
+                let _ = write!(s, "{b:02X}");
+                s
+            });
             eprintln!("asb.derive.aes_key.hex={aes_hex}");
         }
         Ok(out)