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>

Cargo.toml

@@ -278,7 +278,7 @@ percent-encoding = "2.3.2"
 pin-project-lite = "0.2.17"
 pretty_assertions = "1.4.1"
 rand = { version = "0.10.2" }
-ratelimit = "0.10.1"
+ratelimit = "2.0.0"
 rayon = "1.12.0"
 reed-solomon-erasure = { package = "rustfs-erasure-codec", version = "8.0.2" }
 reed-solomon-simd = "3.1.0"