feat: canonical Nim client refactor with typed rows, pool, and allographer wrapper

- Extract wire protocol into clients/nim/src/baradb/wire.nim
- Add BaraError exception hierarchy
- Refactor BaraClient/SyncClient with typedRows, AsyncLock request queue, timeouts, TLS config
- Add BaraPool and optional HTTP fallback
- Add mock-server wire and pool unit tests
- Bump baradb nimble package to 1.2.0
- Make nim-allographer depend on canonical baradb client
- Use typed rows in allographer toJson
- Deprecate src/barabadb/client/client.nim
- Update docs/en/clients.md and clients/nim/README.md

clients/nim/tests/test_pool.nim

@@ -0,0 +1,19 @@
+import std/unittest
+import std/asyncdispatch
+import baradb/client
+import baradb/pool
+
+suite "BaraPool":
+  test "pool stats with one acquired connection":
+    proc run() {.async.} =
+      let cfg = ClientConfig(host: "127.0.0.1", port: 9472, timeoutMs: 100)
+      let pool = newBaraPool(cfg, minConnections = 0, maxConnections = 2)
+      # Without a server, acquire should fail cleanly (timeout or connection refused)
+      var failedCleanly = false
+      try:
+        withClient(pool):
+          discard
+      except BaraError:
+        failedCleanly = true
+      check failedCleanly
+    waitFor run()