tune: lower coalesce/settle step from 40 → 10 ms, raise tunnel-node settle max to 1 s (#674)

The batch coalesce step controls how long the client (and the
tunnel-node's straggler settle) waits between checking for more ops
to pack into the same batch.  At 40 ms the wait was conservative —
good for packing uploads but needlessly slow on the download path
where the tunnel-node round-trip, not coalescing, is the bottleneck.

Lowering the step to 10 ms means we fire batches almost immediately
when there's nothing else queued, cutting ~30 ms of dead air on
every download-dominated round-trip.  When both sides DO have data
in flight (uploads, bursty page loads), the adaptive reset still
works: each arriving op resets the 10 ms step timer, so a rapid
burst naturally coalesces up to the 1 s hard cap without wasting
quota on many small batches.

In short: don't wait when there's nothing to wait for; batch
aggressively when there is.

Client side:
  - DEFAULT_COALESCE_STEP_MS  40 → 10 ms
  - DEFAULT_COALESCE_MAX_MS   unchanged at 1000 ms

Tunnel-node side:
  - STRAGGLER_SETTLE_STEP     40 → 10 ms  (matches client step)
  - STRAGGLER_SETTLE_MAX     500 → 1000 ms (more room to pack
    straggler responses when upstream targets reply at different
    speeds — saves Apps Script quota on the return leg)

Users who prefer the old behaviour can set "coalesce_step_ms": 40
in config.json.

Co-authored-by: yyoyoian-pixel <279225925+yyoyoian-pixel@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/therealaleph/mhrv/ConfigStore.kt

@@ -96,7 +96,7 @@ data class MhrvConfig(
     val verifySsl: Boolean = true,
     val logLevel: String = "info",
     val parallelRelay: Int = 1,
-    val coalesceStepMs: Int = 40,
+    val coalesceStepMs: Int = 10,
     val coalesceMaxMs: Int = 1000,
     val upstreamSocks5: String = "",
 
@@ -210,7 +210,7 @@ data class MhrvConfig(
             put("verify_ssl", verifySsl)
             put("log_level", logLevel)
             put("parallel_relay", parallelRelay)
-            if (coalesceStepMs != 40) put("coalesce_step_ms", coalesceStepMs)
+            if (coalesceStepMs != 10) put("coalesce_step_ms", coalesceStepMs)
             if (coalesceMaxMs != 1000) put("coalesce_max_ms", coalesceMaxMs)
             if (upstreamSocks5.isNotBlank()) {
                 put("upstream_socks5", upstreamSocks5.trim())
@@ -422,7 +422,7 @@ object ConfigStore {
             verifySsl = obj.optBoolean("verify_ssl", true),
             logLevel = obj.optString("log_level", "info"),
             parallelRelay = obj.optInt("parallel_relay", 1),
-            coalesceStepMs = obj.optInt("coalesce_step_ms", 40),
+            coalesceStepMs = obj.optInt("coalesce_step_ms", 10),
             coalesceMaxMs = obj.optInt("coalesce_max_ms", 1000),
             upstreamSocks5 = obj.optString("upstream_socks5", ""),
             passthroughHosts = obj.optJSONArray("passthrough_hosts")?.let { arr ->