9c5af58d51 Consolidate redundant implementations of ParseHashStr (Ben Woosley)
Pull request description:
This change: * adds a length check to all calls to `ParseHashStr`, appropriate given its use to populate a 256-bit number from a hex str * allows the caller to handle the failure, which allows for the more appropriate `JSONRPCError` on failure in `prioritisetransaction` rpc Relative to #14288
Tree-SHA512: baa791147e5ceb3c30c70df3981aaf807bf7d4a90a0be3625540b59aa4b9a9d303a452bfef18bf167cbb833ef9591b4ef5948bf4a1ce67b421d804ae8d20ea53
Backport of Core PR14307
https://github.com/bitcoin/bitcoin/pull/14307/
Depends on D5294