Use elastic multiple search for network stats

[stefangutica]

Reasoning

• GET /network/stats issued four separate Elastic count requests (blocks, accounts, transactions, scResults), one per count.
• They are independent queries with no dependency between them, so _msearch can batch all four into a single HTTP request.

Proposed Changes

• Add IndexerService.getStatsCounts(), backed by one _msearch in ElasticIndexerService, returning all four counts as StatsCounts.
• NetworkService.getStats now makes that single call; the unused AccountService / TransactionService / SmartContractResultService dependencies were dropped.
• Add postNdjson to EsCircuitBreakerProxy: ElasticService.post cannot set headers, and axios corrupts an ndjson body when the content type is application/json. Requests still go through the circuit breaker.
• Pass max_concurrent_searches, otherwise _msearch runs the sub-searches less concurrently than four parallel requests would.
• Cache the unified result under CacheInfo.StatsCounts (1s TTL) to preserve the caching the individual counts had, and keep honouring noCache.

How to test

• GET /network/stats returns the same values as before; counts verified against the four individual _count queries on devnet (blocks, accounts, transactions, scResults all matched).
• Elastic receives one request per second for these counts instead of 2-4 per call.
• GET /network/stats?noCache=true bypasses the cache.
• npm run test -- circuit.breaker.proxy passes.

[github-actions]

k6 load testing comparison.
Base Commit Hash: 8733370
Target Commit Hash: 8fe1076

Metric	Base				Target				Diff
	Avg	Max	90	95	Avg	Max	90	95	Avg	Max	90	95
Mex	23.43	315.83	43.42	55.80	27.01	169.99	36.34	41.32	+15.30% 🔴	-46.18% ✅	-16.32% ✅	-25.95% ✅
Tokens	129.99	1708.02	172.52	252.97	27.13	351.93	36.20	41.42	-79.13% ✅	-79.40% ✅	-79.02% ✅	-83.63% ✅
Blocks	95.66	805.17	155.85	187.28	52.03	10103.56	48.21	59.68	-45.61% ✅	+1154.84% 🔴	-69.06% ✅	-68.13% ✅
Accounts	124.22	469.71	212.38	264.93	199.30	1017.52	336.88	436.66	+60.45% 🔴	+116.63% 🔴	+58.62% 🔴	+64.82% 🔴
Nodes	8567.90	13666.16	13666.09	13666.13	27.07	189.68	36.26	41.40	-99.68% ✅	-98.61% ✅	-99.73% ✅	-99.70% ✅
Transactions	210.12	490.00	488.94	489.24	64.76	13983.27	45.76	67.44	-69.18% ✅	+2753.71% 🔴	-90.64% ✅	-86.22% ✅
Pool	23.54	855.42	42.90	55.95	27.12	383.11	36.24	41.42	+15.19% 🔴	-55.21% ✅	-15.53% ✅	-25.97% ✅
Test Run Duration	60004.10				60003.05

Legend: Avg - Average Response Time, Max - Maximum Response Time, 90 - 90th Percentile, 95 - 95th Percentile
All times are in milliseconds.