Chain stream instead of merge

[RDruon]

Chain stream instead of merging them.

Merge will interleave stream, that's not something we want since it will break prometheus format. See merge documentation at https://docs.rs/tokio-stream/latest/tokio_stream/trait.StreamExt.html#method.merge

Also add a newline to make sure we are printing stats with a separating empty line

From (mind the {operation="open",component="mdt",target="es01a-MDT0000",jobid="node_exporter:989:es-2-virt3-co"}):

[root@node ~]# curl http://localhost:32221/metrics
....
lustre_stats_total{component="mdt",operation="sync",target="es02a-MDT0000"} 6
lustre_stats_total{component="mdt",operation="samedir_rename",target="es02a-MDT0000"} 2
lustre_stats_total{component="mdt",operation="parallel_rename_file",target="es02a-MDT0000"} 2
{operation="open",component="mdt",target="es01a-MDT0000",jobid="node_exporter:989:es-2-virt3-co"} 0
lustre_job_stats_total{operation="close",component="mdt",target="es01a-MDT0000",jobid="node_exporter:989:es-2-virt3-co"} 0
lustre_job_stats_total{operation="mknod",component="mdt",target="es01a-MDT0000",jobid="node_exporter:989:es-2-virt3-co"} 0
....

To:

[root@node ~]# curl http://localhost:32221/metrics
....
lustre_stats_total{component="mdt",operation="sync",target="es02a-MDT0000"} 6
lustre_stats_total{component="mdt",operation="samedir_rename",target="es02a-MDT0000"} 2
lustre_stats_total{component="mdt",operation="parallel_rename_file",target="es02a-MDT0000"} 2

lustre_job_stats_total{operation="open",component="mdt",target="es01a-MDT0000",jobid="node_exporter:989:es-2-virt3-co"} 0
lustre_job_stats_total{operation="close",component="mdt",target="es01a-MDT0000",jobid="node_exporter:989:es-2-virt3-co"} 0
lustre_job_stats_total{operation="mknod",component="mdt",target="es01a-MDT0000",jobid="node_exporter:989:es-2-virt3-co"} 0
...

I haven't been able to reproduce it as part of unit test

[codecov]

Codecov Report

Attention: Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.71%. Comparing base (34615b1) to head (fd007df).
Report is 1 commits behind head on main.

Files	Patch %	Lines
lustrefs-exporter/src/main.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #76      +/-   ##
==========================================
+ Coverage   91.68%   91.71%   +0.03%     
==========================================
  Files          41       41              
  Lines        5207     5228      +21     
  Branches     5207     5228      +21     
==========================================
+ Hits         4774     4795      +21     
  Misses        397      397              
  Partials       36       36              

Flag	Coverage Δ
2_14_0_ddn133	35.26% <ø> (ø)
2_14_0_ddn145	36.01% <ø> (ø)
all-tests	91.71% <96.00%> (+0.03%)	⬆️

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[github-actions]

Benchmark for c1e8a73

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Test	Base	PR	%
jobstats 100	4.2±0.60ms	4.4±0.73ms	+4.76%
jobstats 1000	40.3±5.02ms	43.7±6.71ms	+8.44%

[github-actions]

Benchmark for 113bc57

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Test	Base	PR	%
jobstats 100	4.0±0.62ms	4.3±0.69ms	+7.50%
jobstats 1000	38.6±5.08ms	44.6±6.92ms	+15.54%

[github-actions]

Benchmark for 7b4e669

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Test	Base	PR	%
jobstats 100	4.1±0.62ms	4.4±0.69ms	+7.32%
jobstats 1000	41.8±5.85ms	42.1±6.91ms	+0.72%

[github-actions]

Benchmark for ac5764f

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Test	Base	PR	%
jobstats 100	4.0±0.56ms	4.5±0.78ms	+12.50%
jobstats 1000	39.6±5.42ms	41.3±6.47ms	+4.29%