e7d326f071 Seal extension traits (Tobin C. Harding)
Pull request description:
The extension traits are temporary just while we try to stabalize `primitives`, they are not intended to be implemented by downstream.
Seal the extension traits so that downstream crates cannot implement them.
Fix: #3231
ACKs for top commit:
apoelstra:
ACK e7d326f071a368389f087ddb10ee9bbf3552c33a; successfully ran local tests; thanks! I know this is tedious and annoying
Tree-SHA512: 365979aeabb7941b9c8fa526f71aaadae3ab1cdd6a39e992c5eea2c1057b4b7c2b3a846ffd96a7eab47b9ad4e3e4de4fb141c24c62747e5cee45c74f52f9a172
b4f52ac87a