Cache process/thread id getters and use them in TError origin capture

## Motivation
Profiling the YT master Automaton thread showed TOriginAttributes::Capture (run on every non-OK TError) spending ~60% of its time in a getpid() syscall — uncached on glibc >= 2.25. NYT::GetCurrentThreadId() (gettid) feeds hot thread-affinity / log-manager checks on the same thread.

## Changes
- New library/cpp/yt/system/process_id.* with cached GetProcessId(); GetSystemThreadId() now caches the kernel tid in TLS. Both caches reset in the child after fork.
- Moved thread_name.{h,cpp} from misc to system.
- Removed GetCurrentProcessId/GetCurrentThreadId shims from yt/yt/core/misc/proc.{h,cpp}; migrated all callers to NYT::GetProcessId / NYT::GetSystemThreadId.
- TOriginAttributes::Capture uses the cached getters; recorded Tid is now the real kernel tid (matches perf/ps).
- Added microbenchmarks (library/cpp/yt/system/benchmarks, yt/yt/core/benchmarks/error.cpp).

## Microbenchmarks (release)
| | before | after |
|---|---|---|
| getpid | 101 ns | 0.33 ns |
| gettid | 102 ns | 1.64 ns |
| Capture | 161 ns | 50 ns |
| failed TError | 221 ns | 74 ns |
commit_hash:ee37ae57d61a5a2dd33daee935270f4bb93b7ff9

1 files changed, 35 insertions, 0 deletions

diff --git a/library/cpp/yt/system/benchmarks/process.cpp b/library/cpp/yt/system/benchmarks/process.cpp
new file mode 100644
index 00000000000..74b4b6b1e13
--- /dev/null
+++ b/library/cpp/yt/system/benchmarks/process.cpp
@@ -0,0 +1,35 @@
+#include <benchmark/benchmark.h>
+
+#include <library/cpp/yt/system/process_id.h>
+
+#include <util/system/getpid.h>
+
+namespace NYT {
+namespace {
+
+////////////////////////////////////////////////////////////////////////////////
+
+void BM_GetProcessId(benchmark::State& state)
+{
+    // Cached getpid: only the first call hits the kernel.
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(GetProcessId());
+    }
+}
+
+BENCHMARK(BM_GetProcessId);
+
+void BM_RawGetPid(benchmark::State& state)
+{
+    // Uncached getpid syscall (uncached on glibc >= 2.25), for comparison.
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(::GetPID());
+    }
+}
+
+BENCHMARK(BM_RawGetPid);
+
+////////////////////////////////////////////////////////////////////////////////
+
+} // namespace
+} // namespace NYT