fix(adt): reuse an object's existing open transport on write instead of 409-ing (#144)

[zooloo303]

Summary

Fixes #144. When editing an object that is already captured in an open transport
request of the current user, vsp binds the write to a new request, and SAP
rejects it with:

409 ExceptionResourceLockConflict
Object ... is already locked in request <id> ... cannot be edited under a new request

ADT / Eclipse reuse the lock's existing request automatically. This does the same:
when the caller supplies no transport, fall back to the request SAP already returns
on the LOCK response as LockResult.CorrNr.

Change

New helper resolveWriteTransport(supplied, lockCorrNr, opName)
(pkg/adt/transport_reuse.go), wired in right after the lock in the primary update
entry points:

• WriteProgram, WriteClass (pkg/adt/workflows.go)
• EditSourceWithOptions (pkg/adt/workflows_edit.go)

Safety

The fallback re-runs checkTransportableEdit on the resolved request, so auto-reuse
cannot bypass --allow-transportable-edits or the --allowed-transports
whitelist. An explicitly-supplied transport is used unchanged (already gated at the
top-level mutation gate). A local object (no open request) is unchanged (empty
transport).

Tests

TestResolveWriteTransport covers explicit-wins, local/no-op, fallback-when-allowed,
and the safety-critical case where the fallback is blocked because transportable
edits are disabled. go test ./pkg/adt/... is green.

Verified live against an on-prem system: editing an object already bound to an open
request now succeeds without the caller supplying the transport (previously a
409), and the object is left clean afterwards.

Scope / follow-up

Covers PROG/CLAS full-source writes and surgical EditSource (any object type). The
same one-line reuse applies to writeSourceUpdate (INTF/DDLS/BDEF/SRVD),
writeClassMethodUpdate, and UpdateFromFile — happy to fold those in if you'd
prefer one comprehensive change; kept minimal here for reviewability.

Note: this touches the same write paths as #125 / #108; it composes cleanly with them
(verified by stacking all three locally and exercising the combined path live).