fix mex token previous24hVolume values

[cfaur09]

Reasoning

• The current implementation only takes volume24h from a single pair for each token, which is incorrect
• A token can be traded in multiple pairs (as base or quote token), so its total volume should be the sum of all its pair volumes

Proposed Changes

• Added a tokenVolumes map to track total volume for each token across all pairs
• Modified getAllMexTokensRaw to first calculate aggregated volumes for each token (both as base and quote)
• Updated volume assignment to use the pre-calculated aggregated volumes from tokenVolumes map

How to test

• <api>/mex/tokens/EMR-d10ed9 -> should have correct previous24hVolume value

[github-actions]

k6 load testing comparison.
Base Commit Hash: 10f304b
Target Commit Hash: 41fd3e4

Metric	Base				Target				Diff
	Avg	Max	90	95	Avg	Max	90	95	Avg	Max	90	95
Pool	49.77	457.13	53.96	55.90	48.15	584.60	51.54	53.42	-3.26% ✅	+27.88% 🔴	-4.48% ✅	-4.42% ✅
Mex	49.51	421.53	53.92	55.76	47.82	140.31	51.55	53.46	-3.42% ✅	-66.71% ✅	-4.40% ✅	-4.13% ✅
Tokens	50.09	745.93	54.00	55.82	47.90	348.51	51.53	53.43	-4.37% ✅	-53.28% ✅	-4.56% ✅	-4.28% ✅
Nodes	49.75	444.07	53.93	55.80	48.08	405.92	51.54	53.37	-3.35% ✅	-8.59% ✅	-4.43% ✅	-4.34% ✅
Transactions	61.76	1109.24	54.83	57.40	60.83	1088.17	52.10	54.63	-1.50% ✅	-1.90% ✅	-4.97% ✅	-4.83% ✅
Accounts	50.03	658.03	54.05	55.88	48.04	778.68	51.52	53.49	-3.98% ✅	+18.33% 🔴	-4.69% ✅	-4.27% ✅
Blocks	55.75	1351.86	54.76	57.35	54.62	1375.70	52.04	54.47	-2.04% ✅	+1.76% 🔴	-4.95% ✅	-5.02% ✅
Test Run Duration	60002.47				60005.11

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