Merge bitcoin#26179: bench: Add missed ECCVerifyHandle instance

f09d47b bench: Add missed `ECCVerifyHandle` instance (Hennadii Stepanov)

Pull request description:

  To clearly observe the lack of an `ECCVerifyHandle` instance,
  - apply the following diff:
  ```diff
  --- a/src/Makefile.bench.include
  +++ b/src/Makefile.bench.include
  @@ -19,11 +19,9 @@ bench_bench_bitcoin_SOURCES = \
     bench/bench.h \
     bench/bench_bitcoin.cpp \
     bench/block_assemble.cpp \
  -  bench/ccoins_caching.cpp \
     bench/chacha20.cpp \
     bench/chacha_poly_aead.cpp \
     bench/checkblock.cpp \
  -  bench/checkqueue.cpp \
     bench/crypto_hash.cpp \
     bench/data.cpp \
     bench/data.h \
  @@ -46,8 +44,7 @@ bench_bench_bitcoin_SOURCES = \
     bench/rpc_blockchain.cpp \
     bench/rpc_mempool.cpp \
     bench/strencodings.cpp \
  -  bench/util_time.cpp \
  -  bench/verify_script.cpp
  +  bench/util_time.cpp

   nodist_bench_bench_bitcoin_SOURCES = $(GENERATED_BENCH_FILES)

  ```
  - then
  ```
  $ ./autogen
  $ ./configure
  $ make clean
  $ make
  ```
  - then
  ```
  $ ./src/bench/bench_bitcoin -filter=ExpandDescriptor
  bench_bitcoin: pubkey.cpp:296: bool CPubKey::IsFullyValid() const: Assertion `secp256k1_context_verify && "secp256k1_context_verify must be initialized to use CPubKey."' failed.
  Aborted (core dumped)
  ```

ACKs for top commit:
  achow101:
    ACK f09d47b
  w0xlt:
    ACK bitcoin@f09d47b

Tree-SHA512: e1f33f88d427c57fe31d5810d12e9f46fed2911f5736208ebf7d4a968de0dd8c1f6b73a0d1093316da117dd3bcfda5dde6e41d6c95fcdb99bdea62e19df5ad20

Author: MacroFake

src/bench/descriptors.cpp

@@ -4,6 +4,7 @@
 
 #include <bench/bench.h>
 #include <key.h>
+#include <pubkey.h>
 #include <script/descriptor.h>
 #include <script/standard.h>
 
@@ -12,6 +13,9 @@
 
 static void ExpandDescriptor(benchmark::Bench& bench)
 {
+    const ECCVerifyHandle verify_handle;
+    ECC_Start();
+
     const auto desc_str = "sh(wsh(multi(16,03669b8afcec803a0d323e9a17f3ea8e68e8abe5a278020a929adbec52421adbd0,0260b2003c386519fc9eadf2b5cf124dd8eea4c4e68d5e154050a9346ea98ce600,0362a74e399c39ed5593852a30147f2959b56bb827dfa3e60e464b02ccf87dc5e8,0261345b53de74a4d721ef877c255429961b7e43714171ac06168d7e08c542a8b8,02da72e8b46901a65d4374fe6315538d8f368557dda3a1dcf9ea903f3afe7314c8,0318c82dd0b53fd3a932d16e0ba9e278fcc937c582d5781be626ff16e201f72286,0297ccef1ef99f9d73dec9ad37476ddb232f1238aff877af19e72ba04493361009,02e502cfd5c3f972fe9a3e2a18827820638f96b6f347e54d63deb839011fd5765d,03e687710f0e3ebe81c1037074da939d409c0025f17eb86adb9427d28f0f7ae0e9,02c04d3a5274952acdbc76987f3184b346a483d43be40874624b29e3692c1df5af,02ed06e0f418b5b43a7ec01d1d7d27290fa15f75771cb69b642a51471c29c84acd,036d46073cbb9ffee90473f3da429abc8de7f8751199da44485682a989a4bebb24,02f5d1ff7c9029a80a4e36b9a5497027ef7f3e73384a4a94fbfe7c4e9164eec8bc,02e41deffd1b7cce11cde209a781adcffdabd1b91c0ba0375857a2bfd9302419f3,02d76625f7956a7fc505ab02556c23ee72d832f1bac391bcd2d3abce5710a13d06,0399eb0a5487515802dc14544cf10b3666623762fbed2ec38a3975716e2c29c232)))";
     const std::pair<int64_t, int64_t> range = {0, 1000};
     FlatSigningProvider provider;
@@ -25,6 +29,8 @@ static void ExpandDescriptor(benchmark::Bench& bench)
             assert(success);
         }
     });
+
+    ECC_Stop();
 }
 
 BENCHMARK(ExpandDescriptor);