Add median-time-past (MTP) calculation to CheckPoint #7544

Job	Run time
Rust fmt	13s
prepare	4s
Check no_std	44s
Build & Test (1.88.0, true, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	2m 2s
Build & Test (1.75.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	2m 22s
Build & Test (1.75.0, --all-features)	4m 3s
Build & Test (1.88.0, true, --all-features)	3m 40s
Build & Test (1.63.0, --all-features)	5m 47s
Check WASM	1m 44s
Build & Test (1.63.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	4m 42s
Build & Test Examples (example_electrum)	56s
Rust clippy	1m 23s
Build & Test Examples (example_cli)	35s
Build & Test Examples (example_bitcoind_rpc_polling)	41s
Build & Test Examples (example_esplora)	53s
	29m 49s

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