fix(market-data): deduplicate tick history overlaps

[LimiNode]

Summary

• make tick history-overlap identity configurable per route
• add provider default identity hook; Intrade defaults to timestamp identity
• support timestamp, time-plus-prices, and exact-observation policies
• retain the last delivered timestamp group and remove exact policy matches across inclusive history batches and prefill anchors
• replace quadratic intra-batch deduplication with hash-based lookup
• add cross-batch, provider-default, route-override, and public contract regressions
• synchronize EN/RU Router and API-contract documentation

This fixes duplicate delivery of inclusive history anchors while preserving distinct observations when the selected identity policy considers them distinct.

Chunked initial prefill for max_backfill_ms is intentionally left for the next stacked PR.

Verification

• market_data_subscription_contract_test: 26/26
• market_data_router_test: 23/23
• market_data_continuity_test: 46/46
• market_data_tick_history_contract_test: 8/8
• market_data_tick_continuity_test: 16/16
• intrade_observed_tick_history_test: 7/7
• public umbrella-header C++17 syntax-check: passed
• git diff --check: passed