[AT]: Support a flexible `Data` enum for audit trail record payloads

[itsyaasir]

Feature description

Introduce a flexible Data payload type for audit trails so one trail can store both text and binary record data.

The intended model is to support an enum-like payload shape equivalent to:

enum Data has store + copy + drop {
    Bytes(vector<u8>),
    Text(String),
}

This would allow using AuditTrail<Data> as the default flexible trail shape, while still leaving room for custom payload types where needed.

Motivation

Today an audit trail is generic over one fixed data type. Once a trail is created as AuditTrail<String> or AuditTrail<vector<u8>>, that choice is permanent for all records in that trail.

That makes the trail schema rigid for users who want a mix of text and binary records. The discussed conclusion was that a flexible Data enum would provide a better default experience for Rust and TS users while preserving the generic model for custom Move payload types.

Requirements

1. Introduce a Move payload type equivalent to Data { Bytes(vector<u8>), Text(String) }.
2. Allow AuditTrail<Data> to be used as the flexible/default trail payload type.
3. Preserve support for custom generic payload types, e.g. AuditTrail<MyCustomDataType>.
4. Expose the same flexible Data model consistently in Rust and TS.
5. Keep record add/read APIs aligned across Move, Rust, and TS.

Open questions

Should AuditTrail<Data> become the primary/default path in the SDKs while still allowing advanced users to opt into custom generic payload types?

Are you planning to do it yourself in a pull request?

Yes