test(replication): pin the scanner existing-object compensation matrix (#5877)

P1-20 (rustfs/backlog#1675 B2, test-only). No prior test wrote objects
BEFORE the replication rule arrived, leaving the scanner's existing-object
resync pass — the only channel for such objects — without end-to-end
coverage, and the enqueue truth table partially unpinned at unit level.

e2e (both negative cells are contracts, asserted over multiple fast-scanner
cycles next to a replicated control key that proves the scanner and the
live path are running):
- test_scanner_compensates_existing_objects_across_write_paths: plain PUT,
  CopyObject and Snowball auto-extract products written pre-rule all
  converge via scanner compensation; a null-version object (PUT before the
  bucket became versioned) is pinned as never compensated (the scanner heal
  gate skips nil-version objects).
- test_scanner_never_compensates_when_existing_object_replication_disabled:
  ExistingObjectReplication=Disabled is a contract, not a delay — existing
  keys stay absent while post-rule writes replicate normally.

Unit truth-table pins (crates/replication):
- queue.rs: an empty replicate decision (Disabled existing-object, inbound
  REPLICA) skips heal queueing for every status; Completed without a resync
  decision skips.
- operation.rs: existing-object resync without a reset replicates exactly
  the never-replicated (Empty) objects.

Helper: put_bucket_replication_with_statuses parameterizes the previously
hardcoded ExistingObjectReplication status; the nextest count comments are
refreshed to the post-rebase totals.

.config/nextest.toml

@@ -218,7 +218,7 @@ test-group = 'ecstore-serial-flaky'
 # the nightly profile derives its set as "the replication module MINUS this
 # allowlist", so any new replication test lands in nightly by default (never
 # silently unrun) until it is explicitly blessed as fast here. Keep the two
-# regexes byte-identical. Count invariant: 20 here + 47 nightly = 67 total
+# regexes byte-identical. Count invariant: 20 here + 49 nightly = 69 total
 # (authority: `cargo nextest list`; docs/testing/e2e-suite-inventory.md).
 # HISTORY (2026-07-11): the 20 fast tests were briefly pulled out of this lane
 # (#4724) because they set a loopback (127.0.0.1) replication target that the
@@ -344,7 +344,7 @@ path = "junit.xml"
 #     object_lambda) — too heavy for the merge budget; they run in ci-7's
 #     nightly 4-node lane.
 #   * replication_extension_test — repl-1 already splits it into the PR
-#     `e2e-smoke` (20 fast) and `e2e-repl-nightly` (47 slow) lanes and reserves
+#     `e2e-smoke` (20 fast) and `e2e-repl-nightly` (49 slow) lanes and reserves
 #     it for those, so e2e-full does not double-run it.
 #   * #[ignore]d tests — nextest skips them by default (no --run-ignored); the
 #     manual-localhost:9000 reliant/policy tests are ci-13's migration.