fix(build): support non-Linux Unix targets (illumos/Solaris/*BSD) (#5853)

* fix(build): support non-Linux Unix targets (illumos/Solaris/*BSD)

Two independent build-infrastructure blockers kept RustFS from building on
non-Linux Unix platforms. Neither touches runtime logic.

1. pulsar regenerates its protobuf bindings in build.rs on every build, which
   needs `protoc`. Platforms without a packaged protoc (illumos/Solaris/*BSD)
   now enable pulsar's `protobuf-src` feature via a cfg-gated dependency, which
   builds a vendored protoc from C++ sources. Mainstream targets keep the lean
   dependency and their existing system/CI protoc.

2. clocksource 0.8.3 (pulled in transitively by ratelimit 0.10) used the
   Linux-only `CLOCK_MONOTONIC_COARSE`. ratelimit 2.0 dropped the clocksource
   dependency entirely, so upgrading removes the portability problem at the
   root rather than patching clocksource. The bandwidth throttle's bulk
   `consume()` is rewritten onto ratelimit 2.0's `try_wait_n`, preserving the
   best-effort partial-consumption semantics.

Verified: cargo check + bandwidth monitor unit tests pass; cargo tree confirms
protobuf-src is enabled only for illumos/Solaris/*BSD and clocksource is gone
from the graph. The final illumos build must be confirmed on-platform.

Closes #3195

* fix(ecstore): guard ratelimit v2 capacity overflow

Co-Authored-By: heihutu <heihutu@gmail.com>

* test(ecstore): avoid slow bandwidth reader timeout

Co-Authored-By: heihutu <heihutu@gmail.com>

* fix(targets): drop vendored pulsar protobuf build

Co-Authored-By: heihutu <heihutu@gmail.com>

---------
Co-authored-by: houseme <housemecn@gmail.com>
Co-authored-by: heihutu <heihutu@gmail.com>

crates/ecstore/src/bucket/bandwidth/reader.rs

@@ -306,7 +306,7 @@ mod tests {
     #[tokio::test]
     async fn test_monitored_reader_header_size_accounting() {
         let monitor = Monitor::new(1);
-        monitor.set_bandwidth_limit("b1", "arn1", 100);
+        monitor.set_bandwidth_limit("b1", "arn1", 1_000_000_000);
 
         let data = vec![0u8; 200];
         let inner = TestAsyncReader::new(&data);