Create: Gravity Batteries

One balance fix and the cross-mod convention that generalises it. An 0.1.0 world loads unchanged, and a lone battery on a network behaves exactly as it did.

• A battery no longer winds up on capacity another store is supplying. The round-trip loss makes it impossible for a battery to fund an equal or heavier one -- winding costs weight / efficiency and letting down pays weight -- and that was mistaken for the whole guarantee. A lighter battery costs less than a heavier one supplies, so it was funded. Measured at the defaults: a six block weight filled two three block ones and then spent the rest of itself into a bare shaft. Not perpetual motion, since the transfer loses on the way up like any other winding, but a battery's charge is the player's to spend and nothing should be able to move it uninvited. Capacity supplied by a store is now taken out of the charging test only; a battery deciding whether to let its own weight down goes on counting it, because a discharging store really is holding the network up.
• c:kinetic_energy_storage, a tag any Create addon can honour. The rule above is not about Gravity Batteries, it is about stores, so it is keyed on a tag rather than on this mod's own class: any block in c:kinetic_energy_storage is treated as spending a store rather than generating, and Create already reports how much and whether it is doing it right now. Create: CAES honours it from 0.1.3, so the two mods leave each other's charge alone; a pack author can add a third mod's block with a datapack and fix an interaction neither author has heard of.
• roundTripEfficiency now defaults to 1.0 — a battery gives back exactly what it took in. It was 0.75, on the belief that the loss was what stopped one battery charging another. It never was, and the tag above does that properly and at any setting, which frees this number to be a balance dial. Create charges nothing for a water wheel, a belt or a gearbox, and buffering peaks instead of overbuilding generation is the reason to install a battery at all, so a storage tax was charging for the feature. The knob is still there for packs that want storage to cost something. Existing worlds keep 0.75, because the value is already written to their server config — delete the line, or set it to 1.0, to pick up the new default.
• A battery no longer spends its charge into a network where nothing is drawing. Reported from play: attaching a bare shaft to a charged battery span it up and it lowered its weight to the floor driving nothing. A cogwheel did it too, and so did a disengaged clutch. The guard that was supposed to prevent this asked whether a shaft was attached, which is a much weaker question than whether anything wants power. A battery holding for this reason says "Nothing needs power" rather than reporting the shaft as unpowered. This is not a change to how a battery behaves under partial load — it still supplies its full rating, and sizing the weight to the shortfall is still the player's job.
• c:kinetic_relay is how it tells a load from a pipe, and packs can extend it. The tag lists the blocks that do nothing but pass rotation along — shafts, cogwheels, gearboxes, clutches, gearshifts, chain drives, the encased variants, the gauges — and everything not in it counts as worth driving, so a block from a mod this one has never heard of gets driven rather than ignored. Add your own relay with a datapack. Stress is deliberately not the test: Create gives belts, Gantry Shafts and flywheels an impact of exactly zero, so a battery keyed on stress would have refused to drive a belt network — the most ordinary load in the game.
• Goggles distinguish the two shortfalls: a battery that will not wind because the surplus is borrowed now says so, instead of blaming a network that a Stressometer says has plenty spare.