WIP: CPU network SoA dual-write (not for merge) - #3822

Expand doc/network-soa-phase0.md into the authoritative field-tag, handle,
thread-slice, sidecar, and invalidation spec. Add neuron::container::network
PointProcess and Weight soa storages on Model (Node-style handles), wire
find_container_info/unsorted callbacks, and unit-test that handles survive
permutation.

Add §5.4.1 (target_/src_ as indices/handles, not data_handle) and
§5.5.1 (InputPreSyn deferred; thin gid→fanout after cpu-net-soa).

Embed PointProcess::owning_handle on Point_process and sync Instance/
MechType/ThreadId when prop or _vnt changes. NetCon allocates parallel
Weight SoA rows (heap weight_ stays delivery primary). Unit tests cover
dual-write helpers and PP shell lifetime.

Add network::NetCon storage (Target, WeightIndex, WeightCount, Delay,
Active, SrcPreSyn) on Model. NetCon owns an SoA row and syncs fields on
create/update. HOC weight() steers into Weight SoA data_handles; deliver
mirrors SoA↔heap around pnt_receive so NET_RECEIVE still sees double*.

Add network::PreSyn storage on Model and embed owning handles on PreSyn.
Rebuild a global NetCon* fanout order from dil_ (CoreNEURON-shaped ranges);
send/deliver/fanout iterate that order with dil_ fallback. NetCon::SrcPreSyn
points at the source PreSyn SoA row.

SelfEvent records Weight SoA base index and PointProcess row; net_send
resolves index from NetCon. Delivery uses nrn_pnt_receive_by_weight_index
(M2: SoA→heap→MOD pnt_receive→heap→SoA). NetCon::deliver shares that path.

…ght wipe

Document Phases 0–4 status and known gaps in GROK-NETWORK-SOA.md. Rebuild
PreSyn fanout at NetCvode::init_events (not only on first spike). Stop
soa_sync from copying heap weights over SoA (HOC weight writes). Add
pytest/ctest network_soa_delivery gate for NetStim→ExpSyn.

MOD/nrnivmodl builds only see build/include. Embedding PointProcess
owning_handle forced network/model_data headers that are not installed
there, breaking demo release compiles. Store a non-owning _soa_id on
Point_process; own the SoA row via a map in point.cpp. Add
point_process_access.hpp / nrn_point_process_soa_row for library code.

HOC weight[] is SoA-primary; pnt_receive_init and FOR_NETCONS mutate the
heap. Sync SoA↔heap around INITIAL, and for FOR_NETCONS targets sync all
NetCons sharing the target (including WatchCondition flag delivery).
Fixes hoctests::test_netrec_init_py and external_nrntest FOR_NETCONS/stdp1.

…eliver

Include PointProcess, Weight, NetCon, and PreSyn containers in
nrn_ensure_model_data_are_sorted (thread partition, weight-block repack,
fanout rebuild, cache offsets). On NetCon deliver without FOR_NETCONS,
pass a temporary buffer into pnt_receive instead of the long-lived weight_
heap so SoA stays the source of truth while the heap remains for SaveState
and FOR_NETCONS.

Save NetCon weights from Weight SoA (HOC-primary) and restore into both
heap and SoA so materialize-on-deliver matches SaveState. Resolve SelfEvent
ownership via NetCon object index and weight_index2netcon when the heap
pointer is absent; index2netcon maps all NetCons by HOC index.

Materialize Weight SoA into the heap before BBSaveState weight IO and
mirror heap back to SoA after restore. Match SelfEvents to target NetCons
by heap base or weight_index, and rebind both fields from the DEList
ncindex on restore (same dual-write policy as SaveState).

sort_network_data must resolve HOC point-process objects via
ob2pntproc_0 (dataspace), not this_pointer. NetCon deliver must pass the
long-lived weight_ heap into pnt_receive so MOD net_send(..., _w)
preserves SelfEvent identity for SaveState; resolve owner by weight_index
when needed. Softens SelfEvent savestate_write when no NetCon is found.

Add doc/network-soa/ with L0 README, topology (fanout authority, CoreNEURON
mapping), dual-write/heap roadmap, and sort packing. Point GROK handoff at
the layered map and correct stale short-lived-materialize status text.

Sync Weight SoA when exporting NetCon weights to CoreNEURON and when
returning weights after a CoreNEURON run (HOC weight[] is SoA-primary).
Apply black/clang-format line-wrap fixes for network SoA tests. Merge
with master already on branch for formatting toolchain updates.