feat: support multiple HyperServices instances

[Yaswanth0606]

Summary

Adds a HyperServiceInstance class so an app can run multiple independent HyperServices instances (e.g. several tenants/clients in one session) alongside the existing module-wide singleton API, which is preserved exactly.

import HyperSdkReact, { HyperServiceInstance } from 'hyper-sdk-react';

const instance = new HyperServiceInstance(tenantId, clientId);
eventEmitter.addListener(instance.getHyperEventString(), handler); // per-instance event channel
instance.initiate(payload);
instance.process(payload);
instance.terminate();

What's included

• JS: HyperServiceInstance (create / initiate / process / processWithActivity / openPaymentPage / terminate / onBackPressed / isNull / isInitialised / per-instance merchant views / getHyperEventString), HyperFragmentView instance prop, lazy linking error, platform guards
• Android: keyed native methods with per-key event emission, per-key ProcessActivity callbacks and back-press routing, per-instance merchant views with process-wide fallback, permission/activity-result fan-out to all live instances, invalidate() cleanup on reloads, logcat logging for every skipped call, thread-safe keyed maps
• iOS: mirrored keyed methods, per-key SdkDelegate lifecycle, dynamic supportedEvents, synchronized dict access, invalidate cleanup
• Build fixes: ext.rnVersion Groovy scoping crash (broke newArchEnabled=false consumers), reflective ReactHost (compiles on RN < 0.74), podspec RN-version detection + folly compiler flags
• Docs: full merchant integration guide in the README ("Multiple HyperServices Instances"), including limitations

Verification

• Legacy single-instance behaviour byte-compatible with main (traced API-by-API)
• Multi-agent adversarial review across three rounds; all confirmed findings fixed
• Verified live on an Android emulator and iOS simulator: create → keyed initiate (real SDK boot, session_metadata on the instance channel) → process → payment page rendered → terminate, zero crashes
• javac (full module), clang, tsc, eslint, jest all green

Follow-up PR (stacked): example app modernization + multi-instance demo flows.

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