Update the test wasm tx_write_storage_key to be able to write any arbitrary value

[james-chf]

This PR:

• adds a namada_test_utils crate and a TxWriteData struct which contains a storage key and a value
• renames tx_write_storage_key.wasm to tx_write.wasm
• makes it so that tx_write.wasm can write any value to any key as specified in a TxWriteData

Motivation for this PR is to use it in #886, for writing arbitrary token::Amount values to balance keys in e2e tests.

[james-chf]

I'm not sure where best to put this, it needs to be importable into both the namada_wasm_for_tests and namada_tests crates. Maybe a namada_test_utils crate like in #893, but have put this here for now.

[tzemanovic]

the crate looks like a good idea! In the interim, I think you could put it behind cfg(feature = "testing"), but it's not enabled from wasm_tests yet

[james-chf]

I tried this and having to use namada_core/testing in the namada_wasm_for_tests crate seems to break the wasm build somehow - probably via the pulling in of the rand crate. e.g.

 > make -C wasm_for_tests/wasm_source tx_write
cargo build --release --target wasm32-unknown-unknown --target-dir 'target' --features tx_write && \
        cp "./target/wasm32-unknown-unknown/release/namada_wasm_for_tests.wasm" ../tx_write.wasm
   Compiling num-traits v0.2.15
   Compiling tempfile v3.3.0
   Compiling wait-timeout v0.2.0
error[E0433]: failed to resolve: use of undeclared crate or module `imp`
  --> /Users/main/.cargo/registry/src/github.com-1ecc6299db9ec823/wait-timeout-0.2.0/src/lib.rs:66:9
   |
66 |         imp::wait_timeout(self, dur)
   |         ^^^ use of undeclared crate or module `imp`

For more information about this error, try `rustc --explain E0433`.

I can try out putting this in a namada_test_utils crate now since that should ultimately be less hacky.

[james-chf]

I've put this in a namada_test_utils crate now

[james-chf]

pls update wasm