How should truncate() of local core be handled?

[caolan]

Calling truncate() on the underlying Hypercore seems to cause a few issues:

It can break get() and iteration (and probably other things):

import Hyperbee from './index.js'
import Corestore from 'corestore'

{
    const b = new Hyperbee(new Corestore('./sandbox/store'))
    await b.ready()

    const w = b.write()
    w.tryPut(Buffer.from('1'), Buffer.from('1'))
    await w.flush()

    const w2 = b.write()
    w2.tryPut(Buffer.from('2'), Buffer.from('2'))
    await w2.flush()

    await b.close();
}

{
    const b = new Hyperbee(new Corestore('./sandbox/store'))
    await b.ready()
    await b.core.truncate(1);
    // Does not complete:
    console.log((await b.get(Buffer.from('1'))).value.toString());
    // Never called:
    console.log('done');
    await b.close();
}

Will result in:

Warning: Detected unsettled top-level await at file:///...

But opening the store again after the truncate, it will work again (without key=2 in this case). The unsettled top-level await
it a particularly painful failure mode as you can't catch it with a regular try/catch around the block. The program may just stop running.

Truncating the core also does not emit an 'update' event on the Hyperbee instance when autoUpdate is true. That might be intentional, but if a user re-opens the store there will have been a change without any corresponding update event:

import Hyperbee from './index.js'
import Corestore from 'corestore'

{
    console.log('-- write --');
    const b = new Hyperbee(new Corestore('./sandbox/store', {autoUpdate: true}))
    b.on('update', () => console.log('update'));
    await b.ready()

    const w = b.write()
    w.tryPut(Buffer.from('1'), Buffer.from('1'))
    await w.flush()

    const w2 = b.write()
    w2.tryPut(Buffer.from('2'), Buffer.from('2'))
    await w2.flush()

    console.log((await b.get(Buffer.from('1')))?.value?.toString());
    console.log((await b.get(Buffer.from('2')))?.value?.toString());
    await b.close();
}

{
    console.log('-- truncate --');
    const b = new Hyperbee(new Corestore('./sandbox/store'), {autoUpdate: true})
    b.on('update', () => console.log('update'));
    await b.ready()
    await b.core.truncate(1);
    await b.close();
}

{
    console.log('-- re-open --');
    const b = new Hyperbee(new Corestore('./sandbox/store'), {autoUpdate: true})
    b.on('update', () => console.log('update'));
    await b.ready()
    console.log((await b.get(Buffer.from('1')))?.value?.toString());
    console.log((await b.get(Buffer.from('2')))?.value?.toString());
    await b.close();
}

Will output:

-- write --
update
update
1
2
-- truncate --
-- re-open --
1
undefined