Subxt Metadata: #[no_std] compatibility (#1401)

* no-std tests and porting of subxt-metadata

* update pipeline

* fix generate custom metadata test

* fix cargo run command

* adjust pipeline

* remove prelude from subxt-metadata

* revert autoformatting of Cargo.toml

* remove alloc::format! again, still causes linker errors

* add no-std-build for thumbv7em-none-eabi target

* remove std feature flag

* remove libc and add small readme with test instructions

* change ci for nightly no std

metadata/src/utils/validation.rs

@@ -8,9 +8,10 @@ use crate::{
     CustomMetadata, CustomValueMetadata, ExtrinsicMetadata, Metadata, PalletMetadata,
     RuntimeApiMetadata, RuntimeApiMethodMetadata, StorageEntryMetadata, StorageEntryType,
 };
+use alloc::vec::Vec;
+use hashbrown::HashMap;
 use outer_enum_hashes::OuterEnumHashes;
 use scale_info::{form::PortableForm, Field, PortableRegistry, TypeDef, TypeDefVariant, Variant};
-use std::collections::HashMap;
 
 pub mod outer_enum_hashes;