fix: Convert vendor/pezkuwi-subxt from submodule to regular directory

vendor/pezkuwi-subxt/testing/no-std-tests/.gitignore

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+/target

vendor/pezkuwi-subxt/testing/no-std-tests/Cargo.toml

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+[package]
+name = "subxt-core-no-std-tests"
+edition = "2021"
+publish = false
+version = "0.0.0"
+resolver = "2"
+
+[dependencies]
+subxt-metadata = { path = "../../metadata", default-features = false }
+subxt-core = { path = "../../core", default-features = false }
+subxt-signer = { path = "../../signer", default-features = false, features = ["subxt"] }
+subxt-macro = { path = "../../macro" }
+codec = { package = "parity-scale-codec", version = "3.6.9", default-features = false, features = ["derive"] }
+libc_alloc = { version = "1.0.6" }
+
+[profile.dev]
+panic = "abort"
+
+[profile.release]
+panic = "abort"
+
+# this shouldn't be needed, it's in workspace.exclude, but still
+# I get the complaint unless I add it...
+[workspace]

vendor/pezkuwi-subxt/testing/no-std-tests/README.md

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+# No-Std Testing Crate
+
+To test the no-std compatibility of various subxt-* crates, please run:
+
+```bash
+cargo build --target thumbv7em-none-eabi
+```

vendor/pezkuwi-subxt/testing/no-std-tests/rust-toolchain

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+nightly

vendor/pezkuwi-subxt/testing/no-std-tests/src/main.rs

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+// Copyright 2019-2025 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+#![allow(internal_features)]
+#![feature(lang_items, alloc_error_handler)]
+#![no_std]
+#![no_main]
+
+pub extern "C" fn _start(_argc: isize, _argv: *const *const u8) -> isize {
+    compile_test();
+    0
+}
+
+#[lang = "eh_personality"]
+pub extern "C" fn rust_eh_personality() {}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+use libc_alloc::LibcAlloc;
+
+#[global_allocator]
+static ALLOCATOR: LibcAlloc = LibcAlloc;
+
+//////////////////////////////////////////////////////////////////////////////
+
+extern crate alloc;
+
+/// Including code here makes sure it is not pruned.
+/// We want all code included to compile fine for the `thumbv7em-none-eabi` target.
+fn compile_test() {
+    // Subxt Metadata compiles:
+    use codec::Decode;
+    let bytes: alloc::vec::Vec<u8> = alloc::vec![0, 1, 2, 3, 4];
+    pezkuwi_subxt_metadata::Metadata::decode(&mut &bytes[..]).expect_err("invalid byte sequence");
+
+    const METADATA: &[u8] = include_bytes!("../../../artifacts/polkadot_metadata_small.scale");
+    pezkuwi_subxt_metadata::Metadata::decode(&mut &METADATA[..]).expect("should be valid metadata");
+
+    // Subxt signer compiles (though nothing much works on this particular nostd target...):
+    // Supported targets: <https://docs.rs/getrandom/latest/getrandom/#supported-targets>
+    use core::str::FromStr;
+    let _ = pezkuwi_subxt_signer::SecretUri::from_str("//Alice/bar");
+
+    // Note: sr25519 needs randomness, but `thumbv7em-none-eabi` isn't supported by
+    // `getrandom`, so we can't sign in nostd on this target.
+    //
+    // use pezkuwi_subxt_signer::sr25519;
+    // let keypair = sr25519::dev::alice();
+    // let message = b"Hello!";
+    // let _signature = keypair.sign(message);
+    // let _public_key = keypair.public_key();
+
+    // Note: `ecdsa` is also not compiling for the `thumbv7em-none-eabi` target owing to
+    // an issue compiling `secp256k1-sys`.
+    //
+    // use pezkuwi_subxt_signer::ecdsa;
+    // let keypair = ecdsa::dev::alice();
+    // let message = b"Hello!";
+    // let _signature = keypair.sign(message);
+    // let _public_key = keypair.public_key();
+
+    // Subxt Core compiles:
+    let _era = pezkuwi_subxt_core::utils::Era::Immortal;
+}
+
+#[pezkuwi_subxt_macro::subxt(
+    runtime_metadata_path = "../../artifacts/polkadot_metadata_full.scale",
+    crate = "::pezkuwi_subxt_core"
+)]
+pub mod polkadot {}