chore(cpp): upgrade bazel to 9.1.1

[slbotbm]

Which issue does this PR address?

Closes #
Relates to #

Rationale

dependabot was erroring due to running bazel mod tidy --lockfile_mode=update, which produces a lockfile that cannot be used to build the project correctly in CI. This PR upgrades bazel to 9.1.1, the latest version. This version tolerates bazel mod tidy --lockfile_mode=update's incomplete lockfile update.

What changed?

• upgraded bazel to 9.1.1.
• as a consequence of that, we cannot use the rust toolchain provided on the system, and instead have to download one through bazel.
• this change also surfaced some errors in the test files with regards to comparing incompatible types, and those were corrected.
• haven't updated rules_cc since I want to test if dependabot still errors after this change.

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

If AI tools were used, please answer:

1. Which tools? codex
2. Scope of usage? issue finding and code generation
3. How did you verify the generated code works correctly? read through the code
4. Can you explain every line of the code if asked? yes

[github-actions]

Thanks for the PR. It is labeled S-waiting-on-review and queued for review.

Slash commands (own line, regular comment) move it around the queue:

• /ready - back to S-waiting-on-review after addressing feedback
• /author - flip to S-waiting-on-author while you finish changes
• /request-review @user-or-team - request a reviewer

See CONTRIBUTING.md for details.