[turbopack] Remove incorrect debug_assert in try_read_task_cell (#91699)
### What?
Removes the `debug_assert_not_in_top_level_task` call from
`try_read_task_cell` in `turbopack/crates/turbo-tasks/src/manager.rs`.
### Why?
The assertion was wrong. `debug_assert_not_in_top_level_task` panics
with the message:
> "Eventually consistent read cannot be performed from a top-level
task."
The restriction only applies to **eventually consistent** reads (e.g.
task output reads), which can return stale data if called from a
top-level task (`.run_once(...)`). Cell reads, however, are **strongly
consistent** — they always return up-to-date data. There is no semantic
reason to forbid reading a cell from a top-level task, and the assert
was producing false positives in valid call sites.
### How?
Delete the three lines that guard and invoke
`debug_assert_not_in_top_level_task` inside `try_read_task_cell`. The
function itself and its usage in `try_read_task_output` /
`try_read_local_output` (which are genuinely eventually-consistent) are
unchanged.
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Co-authored-by: Tobias Koppers <sokra@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>