s/Hash/BTree/g in codegen to make the output deterministic

[bolinfest]

We were seeing cases where #[derive(GraphqlQuery)] was not generating
consistent output. This appeared to be due to the use of HashMap and
HashSet, whose iteration order is not guaranteed to be consistent.
Switching to BTreeMap and BTreeSet appears to fix the issue.

[bolinfest]

/cc @tomhoule @LegNeato it looks like an approval is required to run the workflow?

[LegNeato]

👋. Looks good, running CI. Also, hit me up and let's chat, been a long time!

[bolinfest]

@LegNeato indeed, we are long overdue!

I added a commit to the bottom of the stack in this PR to fix the clippy issue caught by CI.

There is also a Prettier issue, but I think the output is also complaining about a bunch of stuff that appears unrelated to my PR.

[bolinfest]

Specifically, this runs with an exit code of 1:

npx prettier --debug-check -l './graphql_client/**/*.graphql'

but based on the output, I'm not clear what it is complaining about.

[bolinfest]

FWIW, as best I can tell, the cargo test failure was a temporary network error when fetching a dependency?

Updating crates.io index
warning: spurious network error (2 tries remaining): SecureTransport error: connection closed via error; class=Net (12)
warning: spurious network error (1 tries remaining): SecureTransport error: connection closed via error; class=Net (12)
error: failed to get `reqwest` as a dependency of package `graphql_client v0.11.0 (/Users/runner/work/graphql-client/graphql-client/graphql_client)`

Caused by:
  failed to load source for dependency `reqwest`

Caused by:
  Unable to update registry `crates-io`

Caused by:
  failed to fetch `https://github.com/rust-lang/crates.io-index`

Caused by:
  network failure seems to have happened
  if a proxy or similar is necessary `net.git-fetch-with-cli` may help here
  https://doc.rust-lang.org/cargo/reference/config.html#netgit-fetch-with-cli

Caused by:
  SecureTransport error: connection closed via error; class=Net ([12](https://github.com/graphql-rust/graphql-client/runs/7782827120#step:4:13))