add robots evicted metric

src/Metrics.zig

@@ -92,6 +92,7 @@ http_navigation_delay_ms: Histogram(&.{
 }) = .{},
 robots_status: CounterEnum("category", @import("network/http.zig").StatusCategory) = .{},
 robots_access: CounterEnum("result", enum { allow, deny }) = .{},
+robots_evictions: Counter = .{},
 cors_check: CounterEnum("result", enum { same_origin, no_cors, simple, preflight }) = .{},
 cors_preflight: CounterEnum("result", enum { allowed, blocked }) = .{},
 cors_response: CounterEnum("result", enum { allowed, blocked }) = .{},
@@ -130,6 +131,7 @@ const help = .{
     .http_navigation_delay_ms = "Time in milliseconds a throttled top-level navigation waited",
     .robots_status = "robots.txt response status",
     .robots_access = "robots.txt result",
+    .robots_evictions = "robots.txt cache entries evicted to stay within limit",
     .cors_check = "CORS initial classification: same_origin/no_cors need no CORS handling, simple needs response validation only, preflight needs an OPTIONS round-trip first",
     .cors_preflight = "CORS preflight (OPTIONS) results, one per request that required one",
     .cors_response = "CORS actual-response validation results",

src/network/Robots.zig

@@ -233,6 +233,7 @@ pub const RobotStore = struct {
 
         if (try self.evictions.insert(gop.key_ptr.*)) |evict_key| {
             if (self.map.fetchRemove(evict_key)) |kv| {
+                lp.metrics.robots_evictions.incr();
                 self.allocator.free(kv.key);
                 var entry = kv.value;
                 self.freeEntry(&entry);