refactor: Traced await

[nameexhaustion]

This is a branch with added tracing to await points in the new-streaming compute nodes, intended for finding which await points are blocking execution in the event of a deadlock.

Compile and run with POLARS_TRACED_AWAIT=1 set in the environment, which should print lines to stderr similar to the following:

The output should be saved to a file, the following script can then be used to extract the locations at which async tasks are currently blocked:

import polars as pl
from pathlib import Path

trace_file = ".env/trace"

df = (
    pl.Series("raw", [Path(trace_file).read_text()])
    .str.strip_chars_end("\n")
    .str.split("\n")
    .list.explode()
    .to_frame()
    .filter(
        pl.first().str.starts_with("begin_await")
        | pl.first().str.starts_with("finish_await")
    )
)

v = (
    df.with_columns(
        pl.col("raw")
        .str.splitn(" ", 3)
        .struct.rename_fields(["event", "id", "location"])
        .struct.unnest()
    )
    .filter(pl.len().over("id") < 2)
    .unique("location")
    .sort("location")
)


with pl.Config(
    tbl_formatting="ASCII_MARKDOWN",
    fmt_str_lengths=999,
    tbl_width_chars=999,
    tbl_hide_column_data_types=True,
    tbl_rows=999,
):
    print(v.select("location"))

[codecov]

Codecov Report

Attention: Patch coverage is 75.72115% with 101 lines in your changes missing coverage. Please review.

Project coverage is 80.59%. Comparing base (33ed4b7) to head (b53ca05).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-stream/src/nodes/merge_sorted.rs	41.17%	20 Missing ⚠️
...src/nodes/io_sources/ndjson/negative_slice_pass.rs	0.00%	13 Missing ⚠️
crates/polars-stream/src/prelude.rs	53.57%	13 Missing ⚠️
crates/polars-stream/src/nodes/with_row_index.rs	0.00%	9 Missing ⚠️
crates/polars-stream/src/nodes/joins/equi_join.rs	71.42%	6 Missing ⚠️
crates/polars-stream/src/nodes/zip.rs	0.00%	6 Missing ⚠️
crates/polars-stream/src/nodes/reduce.rs	0.00%	5 Missing ⚠️
...eam/src/nodes/io_sources/parquet/metadata_utils.rs	33.33%	4 Missing ⚠️
...c/nodes/io_sources/parquet/row_group_data_fetch.rs	50.00%	4 Missing ⚠️
crates/polars-stream/src/nodes/multiplexer.rs	0.00%	4 Missing ⚠️
... and 10 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21638      +/-   ##
==========================================
- Coverage   80.59%   80.59%   -0.01%     
==========================================
  Files        1604     1605       +1     
  Lines      231526   231694     +168     
  Branches     2650     2650              
==========================================
+ Hits       186593   186726     +133     
- Misses      44316    44351      +35     
  Partials      617      617              

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