fix: fix missing orders (#163)

# Description

## Context
@elena-zh create a TWAP tx that didn't get index in watch tower.

https://basescan.org/tx/0xa9e88af5dee1d51f217bbe7613e2897cec6b3d989e8f3cab5142aa74ccb96278#eventlog

I saw there was not logs for that transaction. Which is odd! I can see
the event for conditional order created.
During my test, my transaction was indexed. 

https://basescan.org/tx/0xf0a848e6899330e84e86160f079cf341b145b1fb2bbc2f7a8aec1dfb425384c9#eventlog

In principle both TX emit the same event, and should have been picked in
the same way, but something was making us to skip some indexing of
events

## Cause
I reviewed the code and saw some changes applied 2 months ago were
making us skip the indexing of events for some blocks.

See:
https://github.com/cowprotocol/watch-tower/pull/161/files#r1862591918

## Solution
Bring back the code that skips the polling of tradable orders from the
handlers, but leaves the indexing of conditional orders (so we don't
miss an order creation and we can do the polling in a future block).


<img width="1714" alt="image"
src="https://github.com/user-attachments/assets/ab8f7773-ad07-420c-a9e5-7256a71bb578">

src/services/chain.ts

@@ -320,15 +320,6 @@ export class ChainContext {
     let lastBlockReceived = lastProcessedBlock;
     provider.on("block", async (blockNumber: number) => {
       try {
-        // Decide if we should process this block before polling for events
-        const shouldProcessBlock =
-          blockNumber % this.processEveryNumBlocks === 0;
-
-        if (!shouldProcessBlock) {
-          log.debug(`Skipping block ${blockNumber}`);
-          return;
-        }
-
         log.debug(`New block ${blockNumber}`);
 
         const block = await provider.getBlock(blockNumber);
@@ -453,10 +444,11 @@ async function processBlock(
   blockNumberOverride?: number,
   blockTimestampOverride?: number
 ) {
-  const { provider, chainId } = context;
+  const { provider, chainId, processEveryNumBlocks } = context;
   const timer = metrics.processBlockDurationSeconds
     .labels(context.chainId.toString())
     .startTimer();
+
   const log = getLogger(
     "chainContext:processBlock",
     chainId.toString(),
@@ -482,24 +474,29 @@ async function processBlock(
     }
   }
 
+  // Decide if we should process this block
+  const shouldProcessBlock = block.number % processEveryNumBlocks === 0;
+
   // Check programmatic  orders and place orders if necessary
-  const result = await checkForAndPlaceOrder(
-    context,
-    block,
-    blockNumberOverride,
-    blockTimestampOverride
-  )
-    .then(() => true)
-    .catch(() => {
-      hasErrors = true;
-      log.error(`Error running "checkForAndPlaceOrder" action`);
-      return false;
-    });
-  log.debug(
-    `Result of "checkForAndPlaceOrder" action for block ${
-      block.number
-    }: ${_formatResult(result)}`
-  );
+  if (shouldProcessBlock) {
+    const result = await checkForAndPlaceOrder(
+      context,
+      block,
+      blockNumberOverride,
+      blockTimestampOverride
+    )
+      .then(() => true)
+      .catch(() => {
+        hasErrors = true;
+        log.error(`Error running "checkForAndPlaceOrder" action`);
+        return false;
+      });
+    log.debug(
+      `Result of "checkForAndPlaceOrder" action for block ${
+        block.number
+      }: ${_formatResult(result)}`
+    );
+  }
 
   timer();