optimization: introduce PresaltedSipHasher for repeated hashing

Replaces the `SipHashUint256Extra` function with the `PresaltedSipHasher` class that caches the constant-salted state (v[0-3] after XORing with keys).
This avoids redundant XOR operations when hashing multiple values with the same keys, benefiting use cases like `SaltedOutpointHasher`.

This essentially brings the precalculations in the `CSipHasher` constructor to the `uint256`-specialized SipHash implementation.

> cmake -B build -DBUILD_BENCH=ON -DCMAKE_BUILD_TYPE=Release && cmake --build build -j$(nproc) && build/src/bench/bench_bitcoin -filter='SaltedOutpointHasherBench.*' -min-time=10000

> C++ compiler .......................... AppleClang 16.0.0.16000026

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|               57.27 |       17,462,299.19 |    0.1% |     11.02 | `SaltedOutpointHasherBench_create_set`
|               11.24 |       88,997,888.48 |    0.3% |     11.04 | `SaltedOutpointHasherBench_hash`
|               13.91 |       71,902,014.20 |    0.2% |     11.01 | `SaltedOutpointHasherBench_match`
|               13.29 |       75,230,390.31 |    0.1% |     11.00 | `SaltedOutpointHasherBench_mismatch`

compared to master:
create_set - 17,462,299.19/17,065,922.04 - 2.3% faster
hash       - 88,997,888.48/83,576,684.83 - 6.4% faster
match      - 71,902,014.20/68,985,850.12 - 4.2% faster
mismatch   - 75,230,390.31/71,942,033.47 - 4.5% faster

> C++ compiler .......................... GNU 13.3.0

|               ns/op |                op/s |    err% |          ins/op |          cyc/op |    IPC |         bra/op |   miss% |     total | benchmark
|--------------------:|--------------------:|--------:|----------------:|----------------:|-------:|---------------:|--------:|----------:|:----------
|              135.38 |        7,386,349.49 |    0.0% |        1,078.19 |          486.16 |  2.218 |         119.56 |    1.1% |     11.00 | `SaltedOutpointHasherBench_create_set`
|               23.67 |       42,254,558.08 |    0.0% |          247.01 |           85.01 |  2.906 |           4.00 |    0.0% |     11.00 | `SaltedOutpointHasherBench_hash`
|               58.95 |       16,962,220.14 |    0.1% |          446.55 |          211.74 |  2.109 |          20.86 |    1.4% |     11.01 | `SaltedOutpointHasherBench_match`
|               76.98 |       12,991,047.69 |    0.1% |          548.93 |          276.50 |  1.985 |          20.25 |    2.3% |     10.72 | `SaltedOutpointHasherBench_mismatch`

compared to master:
create_set -  7,386,349.49/7,312,133.16  - 1% faster
hash       - 42,254,558.08/41,978,882.62 - 0.6% faster
match      - 16,962,220.14/16,549,695.42 - 2.4% faster
mismatch   - 12,991,047.69/12,713,595.35 - 2% faster

Co-authored-by: sipa <pieter@wuille.net>

src/test/fuzz/integer.cpp

@@ -119,7 +119,7 @@ FUZZ_TARGET(integer, .init = initialize_integer)
     (void)MillisToTimeval(i64);
     (void)SighashToStr(uch);
     (void)SipHashUint256(u64, u64, u256);
-    (void)SipHashUint256Extra(u64, u64, u256, u32);
+    (void)PresaltedSipHasher(u64, u64)(u256, u32);
     (void)ToLower(ch);
     (void)ToUpper(ch);
     {