spans and annotations lost across copute() boundaries

**Describe the issue**:

**Minimal Complete Verifiable Example**:

This is broken for both sync and async delayed functions. Calling functions directly (removing delayed decorator) preserves spans and annotations.
This is an issue for both local and distributed cluster.

```python
import asyncio
import time

from dask import annotate, delayed, get_annotations
from dask.distributed import LocalCluster
from distributed import span

cluster = LocalCluster(processes=False)
client = cluster.get_client()

def outer(i: int):
with span(str(i)), annotate(also_i=i):
print("annotations before compute", get_annotations())

# inner_async(i).compute(optimize_graph=False)
inner_sync(i).compute(optimize_graph=False)

@delayed
def inner_sync(i: int):
for _ in range(5):
time.sleep(1)

print("task", i, "annotations:", get_annotations())

@delayed
async def inner_async(i: int):
for _ in range(5):
await asyncio.sleep(1)

print("task", i, "annotations:", get_annotations())

client.submit(outer, 1)

time.sleep(2)

client.submit(outer, 2).result()
```

Results in:

```python
annotations before compute {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}, 'also_i': 1}
task 1 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
annotations before compute {'span': {'name': ('2',), 'ids': ('e975dde3-d903-4643-b7ad-ee26f239be78',)}, 'also_i': 2}
task 1 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
task 2 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
task 1 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
task 2 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
task 1 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
task 2 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
task 1 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
task 2 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
task 2 annotations: {'span': {'name': ('1',), 'ids': ('e6f9a463-dbea-42d9-86e9-74348f017677',)}}
```

2 things here:
- annotations got lost after entering delayed
- span `2` did not overwrite span `1` for second task

**Anything else we need to know?**:

There is an issue about lost annotations from 2021: https://github.com/dask/dask/issues/7036
It mentions graph optimization but `optimize_graph=False` does not help.

**Environment**:

- Dask version: `2025.11.0`
- Python version: `3.12`
- Operating System: Linux
- Install method (conda, pip, source): uv