v3.5.0: fix NPC schedules, monster health, mine spawn-in-wall, dropped items

[0Aredjay0]

Summary

Fixes the long-standing "characters disappearing / walking on water / schedules resetting" bug family (multiple open reports on the Nexus bug tracker going back to v3.2.7), plus closes a save-scum exploit and a few correctness gaps found while investigating. Root-caused against the actual decompiled game (1.6.15), not guessed — happy to share the specific game-code references for any of these on request.

• NPC schedules after a mid-day reload. The game precomputes each NPC's daily route from their morning position and replays it with no collision checks. After a mid-day reload, NPCs are standing somewhere else, so the old code's TryLoadSchedule() + clock-advance ordering reset/raced their state, sending them beelining through walls and water or leaving them frozen. Villagers now get a fresh, collision-valid path to their current schedule destination computed from wherever they actually are, and NPCs already at their destination resume idle behavior immediately instead of standing blank.
• Monster health was being deleted on every mid-day save. cleanMonsters() stripped every monster from the world before the real save ran; the game's own save code never touches monsters, so this was a mod-introduced regression, not a vanilla limitation. It let players save-scum out of any fight. Vanilla monsters now save/reload with their current health; monster types from other mods are still excluded (some aren't safe to serialize).
• Fixed a real crash (ArgumentException) on a location's second mid-day save in a session — RestoreMonsters()'s tracking dictionary was only cleared on one code path.
• Player could spawn inside solid rock in mines/Volcano Dungeon. Those floors regenerate a new random layout every entry and were never part of the save file, so a saved tile could be a wall in the new layout. Now validated against the actual location before warping, using the same tile-recovery the game itself uses for a stale mail/warp target.
• Dropped items (loot, quest items, tools/weapons, forage, and resource piles like wood/stone/coal from chopping/mining) no longer vanish on reload. These were never part of the save file by vanilla design (normal saves only happen after the ground is already clear at night).
• Saving no longer corrupts tomorrow's weather (was deleting rain forecasts / corrupting festival-day weather).
• Multiplayer hang fixed — mid-day saving with farmhands connected now shows a clear message instead of freezing the game forever on the vanilla ready-check barrier.
• Skipped the ~1.5s "has been saved" sparkle-text animation during a mid-day save (cosmetic; doesn't touch the actual save-driving logic).
• A handful of smaller correctness fixes: null/farmhand guards on load, re-entrancy guard on save, off-map NPCs (Marlon) no longer saved/restored, CI's dotnet-version fixed to match the net6.0 target, ModBuildConfig bumped to 4.4.0.

Full changelog with more detail is in the README diff.

Test plan

All of the above verified in-game this session on SMAPI 4.3.2 / SDV 1.6.15:

• Mid-day save + reload: NPCs resume schedules cleanly across two consecutive cycles (clean fresh paths, atDest NPCs resuming idle behavior, cross-map walkers routing correctly)
• Damage (don't kill) a monster, mid-day save, reload → present with reduced health
• Descend several mine levels forcing different regenerated layouts, save mid-level each time, reload → always lands on walkable ground
• Drop a stacked/quality item indoors and outdoors, chop a tree and save before collecting the wood, reload → all reappear at the same tile with correct stack/quality, no duplication
• Confirmed the animation skip doesn't affect the underlying save (file write completes normally, multiplayer ready-check path untouched)

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