Context-aware deserializers

[lxsaah]

When deserializing data in connectors (KNX, MQTT, etc.), there's currently no way to access RuntimeContext to generate platform-independent timestamps or access other runtime services.

For example, when receiving KNX telegrams, we'd like to timestamp them using ctx.runtime().now() during deserialization, but deserializers only receive data: &[u8].

Current Limitation

// Current API - no context available
.with_deserializer(|data: &[u8]| {
    records::temperature::knx::from_knx(data, "9/1/0")
})

Monitors have context access, but deserializers don't.

Proposed Solution

Add a context-aware deserializer option:

.with_deserializer_context(|ctx, data: &[u8]| {
    let mut temp = records::temperature::knx::from_knx(data, "9/1/0")?;
    temp.timestamp = ctx.runtime().now(); // Platform-independent timing
    Ok(temp)
})

This would enable:

• Platform-independent timestamps during deserialization
• Access to logging for deserialization diagnostics
• Consistent timing across Embassy and Tokio runtimes

Workarounds Attempted

• Setting timestamps in monitors works but complicates data flow
• Using Debug formatting on Instant works but is hacky
• Deserializers can't access context, making proper timestamps difficult

Would appreciate this feature to keep deserialization logic clean and platform-independent!