Coalesce start and end dates of drafts with the student_ranks history

[BastiDood]

Currently, we display the log entries events in the following pattern:

{#if endDate !== null}
    <li>{endDate}</li>
{/if}
{#each events as event}
    <li>{event}</li>
{/each}
<li>{startDate}</li>

drap/src/routes/history/[draft]/+page.svelte

Lines 81 to 95 in b1435fb

	{#if end !== null}
	{@const { endIsoString, endDateTime } = end}
	<li class="mb-10 ms-6">
	<span
	class="bg-primary-300-600-token ring-primary-900-50-token absolute -start-3 flex size-6 items-center justify-center rounded-full ring-2"
	><Icon src={CalendarDays} class="size-4" theme="micro" /></span
	>
	<h4 class="h4 mb-2"><time datetime={endIsoString}>{endDateTime}</time></h4>
	<ol class="list">
	<li class="card variant-ghost-success px-3 py-1.5">
	<span class="flex-auto">Draft &num;{did} was concluded.</span>
	</li>
	</ol>
	</li>
	{/if}

drap/src/routes/history/[draft]/+page.svelte

Lines 96 to 149 in b1435fb

	{#each entries as [unix, events] (unix)}
	{@const date = fromUnixTime(unix)}
	{@const heading = format(date, 'PPPpp')}
	<li class="mb-10 ms-6">
	<span
	class="bg-primary-300-600-token ring-primary-900-50-token absolute -start-3 flex size-6 items-center justify-center rounded-full ring-2"
	><Icon src={CalendarDays} class="size-4" theme="micro" /></span
	>
	<h4 class="h4 mb-2"><time datetime={date.toISOString()}>{heading}</time></h4>
	<ol class="list">
	{#each events as { is_system, lab_id, round }}
	{#if round !== null}
	{@const ordinal = round + getOrdinalSuffix(round)}
	{#if is_system}
	<li class="card variant-soft-surface px-3 py-1.5">
	<Icon src={Cog} class="size-4" theme="micro" />
	<span class="flex-auto"
	>The system has skipped the <strong class="uppercase">{lab_id}</strong> for the {ordinal}
	round due to insufficient quota and/or zero demand.</span
	>
	</li>
	{:else}
	<li class="card variant-ghost-secondary px-3 py-1.5">
	<Icon src={UserGroup} class="size-4" theme="micro" />
	<span class="flex-auto"
	>The <strong class="uppercase">{lab_id}</strong> has selected their {ordinal} batch
	of draftees.</span
	>
	</li>
	{/if}
	{:else if is_system}
	<li class="card variant-ghost-error px-3 py-1.5">
	<Icon src={ExclamationTriangle} class="size-4" theme="micro" />
	<span class="flex-auto"
	>A system-automated event for the <strong class="uppercase">{lab_id}</strong>
	occurred during a lottery. This should be impossible. Kindly
	<a href="https://github.com/BastiDood/drap/issues/new" class="anchor"
	>file an issue</a
	> and report this bug there.</span
	>
	</li>
	{:else}
	<li class="card variant-ghost-tertiary px-3 py-1.5">
	<Icon src={ArrowPath} class="size-4" theme="micro" />
	<span class="flex-auto"
	>The <strong class="uppercase">{lab_id}</strong> has obtained a batch of draftees from
	the lottery round.</span
	>
	</li>
	{/if}
	{/each}
	</ol>
	</li>
	{/each}

drap/src/routes/history/[draft]/+page.svelte

Lines 150 to 161 in b1435fb

	<li class="mb-10 ms-6">
	<span
	class="bg-primary-300-600-token ring-primary-900-50-token absolute -start-3 flex size-6 items-center justify-center rounded-full ring-2"
	><Icon src={CalendarDays} class="size-4" theme="micro" /></span
	>
	<h4 class="h4 mb-2"><time datetime={startIsoString}>{startDateTime}</time></h4>
	<ol class="list">
	<li class="card variant-ghost-success px-3 py-1.5">
	<span class="flex-auto">Draft &num;{did} was created.</span>
	</li>
	</ol>
	</li>

This setup unfortunately sections off startDate and endDate from the events history. If endDate happens to be the same as the latest event in events, it would not be coalesced; it would be its own entry in the timeline. The solution is to merge the events under a single discriminated union, where the startDate and the endDate variants sandwich the internal events.