iceberg: detect maintenance work per operation (#8639)

* iceberg: detect maintenance work per operation

* iceberg: ignore delete manifests during detection

* iceberg: clean up detection maintenance planning

* iceberg: tighten detection manifest heuristics

* Potential fix for code scanning alert no. 330: Incorrect conversion between integer types

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

* iceberg: tolerate per-operation detection errors

* iceberg: fix fake metadata location versioning

* iceberg: check snapshot expiry before manifest loads

* iceberg: make expire-snapshots switch case explicit

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Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

weed/plugin/worker/iceberg/config.go

@@ -19,6 +19,7 @@ const (
 	defaultTargetFileSizeMB       = 256
 	defaultMinInputFiles          = 5
 	defaultMinManifestsToRewrite  = 5
+	minManifestsToRewrite         = 2
 	defaultOperations             = "all"
 
 	// Metric keys returned by maintenance operations.
@@ -80,8 +81,8 @@ func ParseConfig(values map[string]*plugin_pb.ConfigValue) Config {
 	if cfg.MinInputFiles < 2 {
 		cfg.MinInputFiles = defaultMinInputFiles
 	}
-	if cfg.MinManifestsToRewrite < 2 {
-		cfg.MinManifestsToRewrite = 2
+	if cfg.MinManifestsToRewrite < minManifestsToRewrite {
+		cfg.MinManifestsToRewrite = minManifestsToRewrite
 	}
 
 	return cfg