ci: build RocksDB 8.9.1 from source (Ubuntu 22.04 ships 6.11.4)

PR #10 added a configure-time FATAL_ERROR for RocksDB < 7.4.0 because
the v5.9.24 daemon on DNS2 was built against librocksdb 6.11 and can't
read smsgDB SST files written by newer RocksDB (XXH3 per-block
checksum). The check worked — but it immediately failed CI, because
GitHub's ubuntu-22.04 runners also ship librocksdb-dev 6.11.4.

This is the same drift class the original patch was meant to prevent.

Fix: build RocksDB from source in CI, pinned to 8.9.1 (matching DNS2's
system version). Add scripts/ci/build-rocksdb.sh as a reusable helper
and call it from each of the four Linux jobs (test-linux-unit,
test-linux-sanitizers, build-linux-daemon, build-linux-qt). Drop
librocksdb-dev from the apt-get install (otherwise find_library would
pick up /usr/lib/librocksdb.so.6.11.4 first) and add libsnappy-dev /
libzstd-dev / liblz4-dev (compression libs RocksDB optionally links
against).

MacOS was already passing — Homebrew's rocksdb is current. Windows
was already passing — MSYS2's mingw-w64-rocksdb is at 9.x.

Also fix a cosmetic CMake bug: the version-detect function was setting
RocksDB_VERSION with PARENT_SCOPE only, so the 'Detected RocksDB
version from version.h:' message printed an empty value. Set the local
variable too so the STATUS message reflects the real value.

.github/workflows/build-all.yml

@@ -22,7 +22,15 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y build-essential cmake ninja-build \
             libboost-all-dev libssl-dev libdb++-dev libleveldb-dev \
-            librocksdb-dev libevent-dev libminiupnpc-dev zlib1g-dev
+            libevent-dev libminiupnpc-dev zlib1g-dev \
+            libsnappy-dev liblz4-dev libzstd-dev
+
+      - name: Build RocksDB from source
+        # Ubuntu 22.04's librocksdb-dev is 6.11.4 which CMakeLists.txt now
+        # refuses to configure against (need >= 7.4 for XXH3 per-block
+        # checksum). Build 8.9.1 from source — same version DNS2 ships —
+        # into /usr/local so CMake's find_library picks it up first.
+        run: sudo bash scripts/ci/build-rocksdb.sh
 
       - name: Configure
         run: |
@@ -104,7 +112,11 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y build-essential cmake ninja-build \
             libboost-all-dev libssl-dev libdb++-dev libleveldb-dev \
-            librocksdb-dev libevent-dev libminiupnpc-dev zlib1g-dev
+            libevent-dev libminiupnpc-dev zlib1g-dev \
+            libsnappy-dev liblz4-dev libzstd-dev
+
+      - name: Build RocksDB from source
+        run: sudo bash scripts/ci/build-rocksdb.sh
 
       - name: Configure with sanitizers
         run: |
@@ -389,7 +401,11 @@ jobs:
           sudo apt-get install -y build-essential cmake ninja-build \
             qtbase5-dev qttools5-dev-tools \
             libboost-all-dev libssl-dev libdb++-dev \
-            libleveldb-dev librocksdb-dev libevent-dev libminiupnpc-dev zlib1g-dev
+            libleveldb-dev libevent-dev libminiupnpc-dev zlib1g-dev \
+            libsnappy-dev liblz4-dev libzstd-dev
+
+      - name: Build RocksDB from source
+        run: sudo bash scripts/ci/build-rocksdb.sh
 
       - name: Configure
         run: |
@@ -516,7 +532,11 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y build-essential cmake ninja-build \
             libboost-all-dev libssl-dev libdb++-dev libleveldb-dev \
-            librocksdb-dev libevent-dev libminiupnpc-dev zlib1g-dev
+            libevent-dev libminiupnpc-dev zlib1g-dev \
+            libsnappy-dev liblz4-dev libzstd-dev
+
+      - name: Build RocksDB from source
+        run: sudo bash scripts/ci/build-rocksdb.sh
 
       - name: Configure
         run: |