refactor(generic): allow `int64_t` -> `double` conversion in `to_doub… #352

Job	Run time
windows-msvc-shared (CAPNPROTO)	7m 41s
windows-msvc-shared (PARQUET)	41m 16s
windows-msvc-shared (JSON)	10m 39s
windows-msvc-shared (CBOR)	8m 32s
windows-msvc-shared (AVRO)	7m 18s
windows-msvc-shared (FLEXBUFFERS)	5m 31s
windows-msvc-shared (MSGPACK)	3m 54s
windows-msvc-shared (XML)	4m 7s
windows-msvc-shared (TOML)	4m 35s
windows-msvc-shared (UBJSON)	7m 18s
windows-msvc-shared (YAML)	4m 29s
windows-msvc (FLEXBUFFERS)	5m 11s
windows-msvc (YAML)	4m 48s
windows-msvc (PARQUET)	8m 18s
windows-msvc (UBJSON)	7m 21s
windows-msvc (AVRO)	7m 32s
windows-msvc (CAPNPROTO)	7m 53s
windows-msvc (MSGPACK)	3m 56s
windows-msvc (benchmarks)	8m 16s
windows-msvc (TOML)	4m 9s
windows-msvc (XML)	4m 37s
windows-msvc (CBOR)	8m 34s
windows-msvc (JSON)	8m 26s
	3h 4m 21s

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