core+gui+cli: anticipation/rebuild dates, preserve relative settings

Fixes around the delivery/build/check date handling (karen7 regtest):

- build_will (GUI + CLI) re-anchors date_to_check to the CURRENT heirs'
  earliest future delivery before building, so an anticipated rebuild is no
  longer blocked by the stale old-will anchor (NO_FUTURE_DATE). The checks of
  the existing will keep their anchored date_to_check.
- _sync_locktime_to_built_txs now PRESERVES RELATIVE locktime/threshold
  recipes ("2y"/"150d") in WILL_SETTINGS instead of freezing them to absolute
  timestamps: the anchored comparisons (resolve_locktime_against_tx and
  resolve_date_to_check with built_locktime) already prevent the daily
  invalidate prompt. Absolute values still sync on a genuine automatic
  anticipation.
- Will.remove_stale_wallet_history drops stale wallet-LOCAL will placeholders
  before every (re)build in GUI and CLI so their coins are available again.
- check_willexecutors_and_heirs raises HeirNotFoundException outside the
  count_heirs gate: a shortened relative recipe on a signed will now triggers
  a plain rebuild ("no heirs" only when there really are none).
- is_locktime_below_threshold compares the settings on one reference frame
  (resolve_guard_threshold), no longer against the built-will anchor.

Tests: purge unit + call-site, no-heirs, guard, anticipated-rebuild
end-to-end (GUI) + CLI mirror + fixed_percent_lists_amount unit,
relative-preserve sync; conftest restores electrum.constants.net after each
test (cross-file pollution guard).

tests/test_core_heirs.py

@@ -36,6 +36,7 @@ from bal.core.heirs import (
     is_op_return_address,
     validate_op_return_hex,
 )
+from bal.core.util import Util
 
 # ------------------------------------------------------------------ #
 # Constants
@@ -167,6 +168,32 @@ def test_heirs_amount_to_float():
     assert heirs.amount_to_float("notanumber") == 0.0
 
 
+def test_fixed_percent_lists_uses_build_anchor_for_relative_heirs():
+    """A relative heir must survive the amount filter when the build anchor
+    (``from_locktime``) is recalculated for the anticipated delivery.
+
+    Before the fix, ``build_will`` kept ``date_to_check`` anchored to the OLD
+    (longer) built will; an "1y" heir resolved before that anchor was excluded
+    by the ``cmp <= 0`` filter and the build reported NO_FUTURE_DATE.  With the
+    anchor recomputed for the new locktime (karen7: 2y -> 1y delivery) the
+    "1y" heir is kept.
+    """
+    wallet = FakeWallet()
+    heirs = Heirs(wallet)
+    heirs["carol"] = ["addr1", "100%", "1y"]
+
+    # Stale anchor (old built 2y will still frozen): "1y" is in the past
+    # relative to it -> excluded from the amount calculation.
+    stale_anchor = Util.parse_locktime_string("2y") - 150 * 86400
+    _, _, percent_heirs, _, _ = heirs.fixed_percent_lists_amount(stale_anchor, 500)
+    assert "carol" not in percent_heirs
+
+    # Recalculated anchor for the new (1y) delivery: the heir is retained.
+    new_anchor = Util.parse_locktime_string("1y") - 150 * 86400
+    _, _, percent_heirs, _, _ = heirs.fixed_percent_lists_amount(new_anchor, 500)
+    assert "carol" in percent_heirs
+
+
 # ------------------------------------------------------------------ #
 # Validation (static methods)
 # ------------------------------------------------------------------ #