Merges from Bitcoin up to the v29 branch point

[tomt1664]

Upstream merges to version 29.x.

Fixes to GUIX builds.

Replaced the upstream Bitcoin Core secp256k1 subtree with BlockstreamResearch/secp256k1-zkp master

Fixes to Github Actions CI:

src/CMakeLists.txt:
Added -Wno-error=conditional-uninitialized and -Wno-error=implicit-fallthrough to the elementssimplicity target to suppress AppleClang warning-as-error failures.
Added C_STANDARD 11 to the elementssimplicity target.

src/test/fuzz/CMakeLists.txt:
Added C11 standard and -UNDEBUG -DPRODUCTION compile flags to simplicity_compute_amr.c via set_source_files_properties, with MSVC-conditional /std:c11 vs -std=c11 handling.

src/test/util/random.cpp:
Added g_used_g_prng = false; reset before the assertion in SeedRandomStateForTest to fix a Windows static-init-order false assertion in fuzz tests.

Multiple wallet/rpc source files (httprpc.cpp, setup_common.cpp, signmessage.cpp, i2p.cpp, core_read.cpp, core_write.cpp, wallet/rpc/*.cpp, recentrequeststablemodel.cpp, net.cpp, primitives/confidential.h, wallet/salvage.cpp, init.cpp, test/fuzz/util.h): Wrapped Elements-specific HexStr/DataStream call sites with MakeByteSpan() to resolve MSVC strict overload resolution failures on vector to Span conversions.

src/assetsdir.cpp:
Replaced boost::split with std::string::find-based parsing to remove the Windows Boost dependency.

Multiple fuzz test source files (p2p_headers_presync.cpp, package_eval.cpp, txdownloadman.cpp, test/fuzz/util/wallet.h, wallet/test/fuzz/spend.cpp, notifications.cpp, witness_program.cpp):
Fixed Elements API divergences from Bitcoin Core in fuzz targets: confidential asset/value types, witness access patterns, and a C4806 sign-conversion fix via static_cast<uint8_t>.

ci/test/03_test_script.sh:
Reworked for NO_DEPENDS branch with CMAKE_GENERATOR fix and corrected script paths.

.github/workflows/ci.yml (win64-native job):
Added -DCMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE to flatten binary output to build/bin/ with no Release/ subdirectory.
Updated functional test env vars to use correct elementsd.exe, elements-cli.exe, elements-util.exe, elements-wallet.exe paths.
Updated fuzz job BITCOINFUZZ to build\bin\fuzz.exe.
Switched fuzz corpora clone from bitcoin-core/qa-assets to ElementsProject/qa-assets, fixing coins_view fuzz assertion failures caused by using Bitcoin-only corpus.

test/functional/feature_trim_headers.py:
Fixed line 269: TrimHeadersTest(file).main().

src/blind.cpp:
Replaced fixed-size 640KB stack arrays unsigned char blind[10000][32] and unsigned char asset_blind[10000][32] with heap-allocated std::vector<std::array<unsigned char, 32>> sized to num_to_blind, eliminating a stack overflow on macOS arm64 worker threads.

test/functional/feature_config_args.py:
Cherry-picked upstream Bitcoin Core commit a306048: added self.extra_args = [["-prune=550"]] in set_test_params() and simplified test_testnet3_deprecation_msg.
Fixed test_config_file_log to write elements.conf directly to default_datadir / "elements.conf".
Stripped -prune= from node.args in test_config_file_log.
Added explicit -prune=550 to both start_node calls in test_testnet3_deprecation_msg.

test/functional/test_framework/util.py:
Fixed get_temp_default_datadir to return temp_dir / ".elements" on macOS instead of temp_dir / "Library/Application Support/Elements".

[delta1]

Github is falling over but looks like there are merge conflicts. Probably need to merge the latest PRs from Elements side first?

[delta1]

Build is failing in a few places now with

 error: ‘OMITTED_NAMED_ARG’ is not a member of ‘RPCArg::Optional’
 1863 |                                     {"pegin_bitcoin_tx", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED_NAMED_ARG, "(only for pegin inputs) The raw bitcoin transaction (in hex) depositing bitcoin to the mainchain_address generated by getpeginaddress"},