With respect to `std::unordered_map` documentation, the `Hash` type
defined in the template is over the `Key` and not `T`, the value. This
hasher is incorrectly named as the `FilterHeader` is the value within this map.
I consider this a bug as opposed to a refactor as the key and value
relationship is implied to be `filter header -> block hash` when it is
the opposite.
Further, the hasher for the key already exists via `BlockHasher`.
ref: https://en.cppreference.com/w/cpp/container/unordered_map.html
Suggested by @l0rinc in #34004
Message by @l0rinc:
This adds a consteval constructor to transaction_identifier (Txid/Wtxid) to allow parsing hex strings at compile-time.
This replaces runtime FromHex checks in tests, ensuring that malformed hardcoded hashes cause build failures rather than runtime test failures.
Test variables are explicitly marked constexpr. This is required to workaround a regression in GCC 14 (Bug 117501) where the compiler incorrectly flags consteval initialization of non-constexpr variables as "statements with no effect".
GCC Bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117501
Reproducer: https://godbolt.org/z/xb5TMaPs6
Co-authored-by: l0rinc <pap.lorinc@gmail.com>
rustaceanrob