fix(ci): bump apt-get timeout 300→600 in nightly workflows (#125)

The 2026-06-18 nightly diff-fuzz run failed at the C++ build deps step
with exit code 124. The job had been running ~5 minutes (16:49 → 16:54
UTC), which matches `timeout 300` exactly:

```
16:49:29 Run timeout 300 sudo apt-get update + timeout 300 sudo apt-get install ...
16:54:09 Get:4 cmake-data (2155 kB)
16:54:26 Get:5 cmake amd64 (11.2 MB)
16:54:36 exit code 124
```

The previous 10 nightly runs took 4:30~4:50 hours total, so the global
job budget (`timeout-minutes: 355` + `timeout 340m` on the fuzz step)
was nowhere near being hit. The failure is purely the apt step's
per-command guard tripping during a slow Azure mirror cycle.

Bump `timeout 300` → `600` on both `apt-get update` and
`apt-get install` in nightly-diff-fuzz.yml and nightly-benchmark.yml
(both have the identical idiom). 600s = 10 minutes is still a hard
ceiling, just lenient enough to absorb the kind of mirror congestion
the 06-18 run hit (cmake 11.2 MB alone took ~17s post-cmake-data, both
combined ran over 5 minutes).

Closes #125.

Does not address #109 / #124 — those are a separate go-vs-cpp
column/row-store divergence pattern that needs root-cause investigation
beyond infra fixes.

Author: Liam0205

.github/workflows/nightly-benchmark.yml

@@ -44,8 +44,8 @@ jobs:
 
       - name: Install system deps
         run: |
-          timeout 300 sudo apt-get update
-          timeout 300 sudo apt-get install -y --no-install-recommends \
+          timeout 600 sudo apt-get update
+          timeout 600 sudo apt-get install -y --no-install-recommends \
             cmake build-essential libluajit-5.1-dev libcurl4-openssl-dev
 
       - name: Install hey

.github/workflows/nightly-diff-fuzz.yml

@@ -49,8 +49,8 @@ jobs:
 
       - name: Install C++ build deps
         run: |
-          timeout 300 sudo apt-get update
-          timeout 300 sudo apt-get install -y --no-install-recommends \
+          timeout 600 sudo apt-get update
+          timeout 600 sudo apt-get install -y --no-install-recommends \
             cmake ninja-build g++-13 libluajit-5.1-dev libcurl4-openssl-dev
 
       - name: Build Go binary