feat(wirings): bounded-state tier DataStream wiring + demo (stacks on #6)

[estebanzimanyi]

Second of four planned tier-specific wiring follow-ups on PR #5's generated MEOS facade. Stacks on PR #6 (stateless wirings). Adds the bounded-state tier.

What's in this PR

File	Purpose
MeosBoundedStateMap<K, IN, OUT>	Generic KeyedProcessFunction with ValueState<byte[]> per key — wraps any bounded-state MeosOps call as a per-key MEOS-handle accumulator
demo/MeosBoundedStateDemoJob	Runnable per-vehicle running-tbox-union pipeline (6 events × 2 vehicles); demonstrates per-key isolation, first-event-null correctness, and checkpoint-safe state
README.md	bounded-state row marked ✅ shipped

Design — state crosses the boundary as bytes, not Pointer

A jnr.ffi.Pointer is a raw native-memory address. Storing one in Flink's ValueState would be a correctness time-bomb — pointers don't survive checkpoints, savepoints, or operator-instance rescaling. So MeosBoundedStateMap keeps state as byte[] (MEOS-WKB or MEOS-WKT, adopter's choice) with three adopter-supplied lambdas mediating the round-trip through MEOS:

byte[] state                  -- the per-key serialized MEOS value (in checkpoint)
    ↓ deserialize (bytes → Pointer)
Pointer prev                  -- the in-flight MEOS handle
    ↓ step(prev, event) → (newPointer, output)
Pointer next, OUT out         -- the new in-flight handle + per-event output
    ↓ serialize (Pointer → bytes)
byte[] newState               -- the per-key serialized new MEOS value (back to checkpoint)

The first event for a key sees prior == null (no state yet); the wiring handles that case by skipping deserialize and letting the step seed state with the first event's result. Same serde discipline MobilityDuck's persistent state machines use.

Tier coverage now (PR #6 + this PR)

Tier	Method count (v4 baseline)	Wirable through
stateless	804	MeosStatelessMap / MeosStatelessFilter (PR #6)
bounded-state	797	MeosBoundedStateMap (this PR)
windowed	161	next follow-up (MeosWindowedAggregate)
cross-stream	140	next follow-up (MeosCrossStreamJoin)
io-meta	195	covered transitively by MeosStatelessMap (no state, no window)
sequence-only	14	n/a — inherently non-streamable

Cumulative: ~1,800 of PR #5's 2,097 generated methods (86%) are now wirable through 3 generic classes (Map + Filter + BoundedStateMap), without per-method registration.

Demo highlights

MeosBoundedStateDemoJob is a 6-event × 2-vehicle pipeline that computes a per-vehicle running tbox union via MeosOpsFreeCore.union_tbox_tbox. State holds the MEOS-WKT text of the current union; each event:

1. Deserializes the prior state via MeosOpsTBox.tbox_in (or null on first event).
2. Calls union_tbox_tbox(prior, eventTbox, 0) (skipping the call entirely when prior is null).
3. Serializes the new state via MeosOpsTBox.tbox_out(newUnion, 6).
4. Emits (vehicleId, runningUnionWKT).

Output (when run with libmeos available): 6 lines, monotonically growing per-vehicle union tboxes, vehicle 1's state independent of vehicle 2's.

Stacking

This PR stacks on feat/flink-stateless-tier-wirings (PR #6). Additive-only: 3 file changes (1 new wiring class + 1 new demo + 1 README row marked ✅). No existing file is touched beyond the README row.

Compile verification

Locally green: 135 .class files total (129 from PR #6 base + 6 new — 1 wiring class + 3 nested lambda interfaces + MeosStep tuple + 1 demo class).