feat(node): implement performance.nodeTiming and uvMetricsInfo

[bartlomieju]

Summary

Closes #31085

Implements performance.nodeTiming from node:perf_hooks with a proper PerformanceNodeTiming class instead of the empty object stub ({}).

Before

import { performance } from 'node:perf_hooks';
setImmediate(() => console.log(performance.nodeTiming.uvMetricsInfo));
// undefined

After

import { performance } from 'node:perf_hooks';
setImmediate(() => console.log(performance.nodeTiming.uvMetricsInfo));
// { loopCount: 1, events: 0, eventsWaiting: 0 }

Changes

deno_core (libs/core/uv_compat.rs, libs/core/runtime/jsruntime.rs):

• Add loop_count, events, events_waiting counters to UvLoopInner
• loop_count increments each event loop iteration
• events increments per TCP/TTY I/O event processed
• Expose via uv_loop_metrics_info() public function

ext/node (ops/perf_hooks.rs, lib.rs):

• Add op_node_uv_metrics_info op that reads counters from UvLoop in OpState

ext/node (polyfills/perf_hooks.js):

• Replace performance.nodeTiming = {} with PerformanceNodeTiming class
• Properties: name, entryType, startTime, duration, timing milestones, loopStart, loopExit, idleTime, uvMetricsInfo, toJSON()
• uvMetricsInfo getter returns real { loopCount, events, eventsWaiting }

Still stubbed/approximated

• Timing milestones (nodeStart, v8Start, environment, bootstrapComplete) are approximated
• idleTime returns 0 (needs idle time tracking in UvLoopInner)
• loopExit returns -1 (needs process exit hook)
• events_waiting counter is not yet incremented

Test plan

• Manual: performance.nodeTiming.uvMetricsInfo returns object with correct shape
• Manual: loopCount increments after event loop iterations
• cargo check passes

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