cargo-bazel: fix binary targets of proc-macro crates using wrong dep attribute (#3975)

## Problem

When a crate has both a `rust_proc_macro` library target and
`rust_binary` targets (e.g. development utilities shipped alongside the
proc-macro), `make_rust_binary` unconditionally places the library in
`deps`. However, rules_rust validates that proc-macro libraries must
appear in `proc_macro_deps`, not `deps`. This causes analysis failures
for any such crate.

## Solution

In `make_rust_binary`, detect whether the crate's library target is a
proc-macro by checking if `Rule::ProcMacro(_)` is present in
`krate.targets`. If it is, insert the library label into
`proc_macro_deps` instead of `deps`.

## Testing
- `binary_of_proc_macro_crate_uses_proc_macro_deps`: verifies that the
generated `rust_binary` has the `proc-macr`o lib in `proc_macro_deps`
and not in `deps`.

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Signed-off-by: Thomas Lam <thomaslam@canva.com>