feat(net): invio/ping/download verso Will-Executor in parallelo (anti-freeze)

Problema: i server Will-Executor venivano contattati in sequenza e, su
timeout, send_request riprovava 10x con sleep 3s (~130s per server morto).
Un solo server irraggiungibile bloccava l'intera operazione (impallamento UI).

Soluzione:
- ThreadPoolExecutor: ping e push ora in parallelo (tempo ~= server piu' lento,
  non la somma). Un server morto non blocca piu' gli altri.
- Fast-fail per operazioni interattive (ping/info/download): max_retries=0,
  niente retry-storm.
- Feedback live: callback on_each() aggiorna il dialog server-per-server
  (thread-safe via pyqtSignal di BalWaitingDialog.update).
- Push transazioni: parallelo ma con retry per-server mantenuti (no perdita tx).

File:
- bal/core/willexecutors.py: send_request(+max_retries,+retry_sleep),
  get_info_task fast-fail, NEW ping_servers_parallel(), push_transactions_parallel(),
  DEFAULT_TIMEOUT=5.
- bal/gui/qt/window.py: ping_willexecutors_task + push_transactions_to_willexecutors
  riscritti su helper paralleli con feedback live; fetch_will_executors_list fast-fail.
- bal/core/util.py: BUGFIX get_value_amount usava in_output (bool) invece di
  din_output (tupla) -> TypeError. Scoperto dai test ufficiali Gitea.

Test (contro il codice refactor):
- pytest tests/ ufficiali: 117 core + 65 gui = 182 passed.
- smoke/external_zip/windows_overflow/gui_fixes: OK.
- parallel_ping_test (nuovo): 0.50s per 8 server vs ~4.00s sequenziale.
- ruff: nessun nuovo problema introdotto (codice nuovo PEP8-compliant).

Aggiunti i test ufficiali del repo Gitea + REPORT_NETWORKING_PARALLELO.md.

tests/test_gui_common.py

@@ -0,0 +1,102 @@
+"""
+Tests for ``bal.gui.qt.common``.
+
+Covers shown_cv, CheckAliveError, add_widget, log_error, export_meta_gui.
+
+Run:
+    QT_QPA_PLATFORM=offscreen python3 tests/test_gui_common.py
+"""
+
+import sys
+sys.path.insert(0, __file__.rsplit("/", 2)[0])
+
+from PyQt6.QtWidgets import QApplication, QGridLayout, QLabel, QWidget
+
+# Import the module itself, not via "from .common import *"
+import bal.gui.qt.common as C
+
+_app = QApplication.instance() or QApplication(sys.argv)
+
+
+# ------------------------------------------------------------------ #
+# shown_cv
+# ------------------------------------------------------------------ #
+
+def test_shown_cv_default():
+    cv = C.shown_cv(True)
+    assert cv.get() is True
+
+
+def test_shown_cv_set():
+    cv = C.shown_cv(True)
+    cv.set(False)
+    assert cv.get() is False
+
+
+def test_shown_cv_roundtrip():
+    cv = C.shown_cv(False)
+    assert cv.get() is False
+    cv.set(True)
+    assert cv.get() is True
+    cv.set(True)
+    assert cv.get() is True
+
+
+# ------------------------------------------------------------------ #
+# CheckAliveError
+# ------------------------------------------------------------------ #
+
+def test_check_alive_error_default():
+    err = C.CheckAliveError(1000000)
+    assert err.timestamp_to_check == 1000000
+
+
+def test_check_alive_error_str():
+    err = C.CheckAliveError(1000000)
+    s = str(err)
+    assert "Check alive expired" in s
+    assert "1970" in s
+
+
+def test_check_alive_error_subclass():
+    assert issubclass(C.CheckAliveError, Exception)
+
+
+# ------------------------------------------------------------------ #
+# add_widget
+# ------------------------------------------------------------------ #
+
+def test_add_widget():
+    grid = QGridLayout()
+    parent = QWidget()
+    label = QLabel("test")
+    C.add_widget(grid, "Label", label, 0, "Help text")
+    assert grid.count() == 3  # label + widget + help button
+
+
+def test_add_widget_multiple_rows():
+    grid = QGridLayout()
+    parent = QWidget()
+    C.add_widget(grid, "A", QLabel("a"), 0, "help_a")
+    C.add_widget(grid, "B", QLabel("b"), 1, "help_b")
+    assert grid.count() == 6
+
+
+# ------------------------------------------------------------------ #
+# log_error
+# ------------------------------------------------------------------ #
+
+def test_log_error_no_window():
+    C.log_error((Exception, Exception("test"), None))
+
+
+# ------------------------------------------------------------------ #
+# Main
+# ------------------------------------------------------------------ #
+
+if __name__ == "__main__":
+    for name in sorted(dir()):
+        if name.startswith("test_"):
+            globals()[name]()
+            print(f"  [OK] {name}")
+    print("[OK] All common tests passed")