feat: events metering and quotas (PUT-1683)

[Salazareo]

Stacked on DS/put-1682 — review only this PR's diff; merges bottom-up.

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	93.88% ⬆️ +0.12%	26803 / 28548
🔵	Statements	92.01% ⬆️ +0.01%	29045 / 31565
🔵	Functions	90.17% ⬆️ +0.16%	4807 / 5331
🔵	Branches	80.75% ⬆️ +0.10%	19235 / 23819

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/backend/controllers/events/limits.ts	100%	100%	100%	100%
src/backend/services/events/EventsService.ts	88.21%	81.51%	92.18%	93.21%	563-566, 687, 705-708, 734-737, 743, 749, 762-765, 783, 842, 861, 924, 948, 970-971, 986, 1022, 1024, 1029, 1050, 1052, 1074, 1152, 1156-1157, 1173, 1178, 1202, 1207, 1234, 1236, 1240, 1247, 1296-1299, 1301-1304, 1309-1312, 1347, 1367, 1387-1391, 1423-1427, 1458, 1473, 1485, 1504, 1516, 1518, 1529, 1541, 1560, 1573, 1608-1609, 1635, 1643, 1668, 1691, 1693, 1698, 1708, 1719, 1725, 1808, 1833, 1845-1849, 1867-1868, 1886, 1929-1931, 1966, 2019, 2040, 2063, 2093, 2096, 2097, 2102, 2127, 2245, 2301, 2370, 2379, 2390, 2396, 2439-2440, 2525, 2531, 2574, 2580, 2616-2620, 2642, 2650, 2658, 2668, 2744-2747, 2807, 2861, 2921-2925, 2984, 2995-3000, 3096, 3119, 3133, 3178, 3181, 3191, 3204, 3217-3218, 3246, 3279, 3288-3289, 3386, 3435-3437, 3448-3455, 3465-3466, 3476-3477
src/backend/services/events/costs.ts	100%	100%	100%	100%
src/backend/stores/events/DurableSubscriptionStore.ts	94.35%	86.91%	93.47%	96.31%	208, 212, 362, 387, 406, 676-695, 724-737
src/backend/stores/events/PendingDeliveryStore.ts	93.59%	80%	97.14%	96.53%	147, 238-239, 259, 427, 438, 459, 579, 599, 621-623, 628

Generated in workflow #942 for commit 0cddcc6 by the Vitest Coverage Report Action