fix: unsubscribe data loader on chart destroy

[NemeZZiZZ]

Problem

Store.destroy() never unsubscribes the data loader. _processDataUnsubscribe() is called only from resetData() (verified: it is the single call site in src/).

After dispose(), a live subscribeBar callback keeps firing into the dead store:

subscribeBar.callback(bar)
  → Store._addData(bar, 'update')        // Store.ts
  → _adjustVisibleRange()                // bar is appended
  → _chart.layout({ ... })               // layout scheduled on a destroyed chart

Impact

For the standard realtime setup (setDataLoader with subscribeBar) + dispose(): the subscription keeps pushing bars into the destroyed chart's store — _dataList grows without bound, CPU is spent on every tick, and layout is scheduled on a dead chart. The loader's unsubscribeBar is never given the chance to run.

Fix

Call _processDataUnsubscribe() at the start of Store.destroy(), mirroring resetData(). The method already no-ops safely when loader/symbol/period are missing and uses unsubscribeBar?.() for loaders without it.

One line, one file.