Merge rust-bitcoin/rust-miniscript#778: cleanups: Eliminate `errstr` … #2120

Job	Run time
Bench - nightly toolchain (recent)	3m 12s
Embedded	1m 15s
Docs - stable toolchain (recent)	42s
Docs - nightly toolchain (recent)	40s
Format - nightly toolchain	13s
Integration tests - stable toolchain (26_0)	1m 14s
Lint - nightly toolchain (recent)	44s
Integration tests - stable toolchain (25_2)	1m 2s
Test - 1.63.0 toolchain (minimal)	26m 2s
Integration tests - stable toolchain (25_1)	1m 5s
Test - nightly toolchain (minimal)	14m 51s
Test - 1.63.0 toolchain (recent)	27m 7s
Integration tests - stable toolchain (25_0)	58s
Test - nightly toolchain (recent)	14m 28s
Test - stable toolchain (minimal)	16m 21s
Integration tests - stable toolchain (24_2)	54s
Integration tests - stable toolchain (24_1)	1m 11s
Test - stable toolchain (recent)	16m 18s
Integration tests - stable toolchain (24_0_1)	49s
Integration tests - stable toolchain (23_2)	55s
Integration tests - stable toolchain (23_1)	1m 5s
Integration tests - stable toolchain (23_0)	53s
Integration tests - stable toolchain (22_1)	58s
Integration tests - stable toolchain (22_0)	49s
Integration tests - stable toolchain (0_21_2)	55s
Integration tests - stable toolchain (0_20_2)	47s
Integration tests - stable toolchain (0_19_1)	49s
Integration tests - stable toolchain (0_18_1)	54s
Integration tests - stable toolchain (0_17_1)	54s
	2h 18m 5s

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