feat(pyamber): keep peek side effect free

[carloea2]

What changes were proposed in this PR?

Scan subqueues with a local index when peeking so observation does not advance the round-robin cursor or alter the next message returned by get().

Any related issues, documentation, discussions?

Closes #8225

How was this PR tested?

python -c "import sys,pytest; sys.path[:0]=[worktree amber source, main amber source]; raise SystemExit(pytest.main(['amber/src/test/python/core/util/customized_queue/test_linked_blocking_multi_queue.py','amber/src/test/python/core/models/test_internal_queue.py','-q','-p','no:cacheprovider']))"
76 passed, 1 xfailed

ruff check amber/src/main/python amber/src/test/python
All checks passed

ruff format --check amber/src/main/python amber/src/test/python
213 files already formatted

A direct post-fix probe confirmed that peek does not change the cursor or the next message:

cursor_before_peek=0
peek=second
cursor_after_peek=0
next_after_peek=first

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Codex

[github-actions]

Backport auto-label report

This fix: PR was checked against each actively-supported release branch. release/* labels drive the post-merge backport, so add or remove one to change where this fix lands.

Release branch	Analysis
⚠️ release/v1.3	Not labeled automatically — none of the files this PR modifies exist on this branch (amber/src/main/python/core/util/customized_queue/linked_blocking_multi_queue.py, amber/src/test/python/core/util/customized_queue/test_linked_blocking_multi_queue.py). The fix may target code that isn't on this release, or the files were moved/renamed after the branch was cut. Please check and add release/v1.3 by hand if this fix should be backported here.
✅ release/v1.2	Already labeled — this fix is queued to backport here.

Auto-label run.

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• Contributors with relevant context: @mengw15
  You can notify them by mentioning @mengw15 in a comment.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.91%. Comparing base (70c2114) to head (e332a14).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8226      +/-   ##
============================================
- Coverage     93.94%   93.91%   -0.04%     
  Complexity     4759     4759              
============================================
  Files          1185     1185              
  Lines         48069    48810     +741     
  Branches       5359     5359              
============================================
+ Hits          45159    45838     +679     
- Misses         1480     1542      +62     
  Partials       1430     1430              

Flag	Coverage Δ		*Carryforward flag
access-control-service	81.00% <ø> (ø)		Carriedforward from 70c2114
agent-service	99.32% <ø> (ø)		Carriedforward from 70c2114
amber	89.99% <ø> (ø)		Carriedforward from 70c2114
computing-unit-managing-service	73.67% <ø> (ø)		Carriedforward from 70c2114
config-service	86.86% <ø> (ø)		Carriedforward from 70c2114
file-service	87.91% <ø> (ø)		Carriedforward from 70c2114
frontend	96.49% <ø> (ø)		Carriedforward from 70c2114
notebook-migration-service	79.31% <ø> (ø)		Carriedforward from 70c2114
pyamber	97.87% <100.00%> (-1.01%)	⬇️
workflow-compiling-service	77.19% <ø> (ø)		Carriedforward from 70c2114

*This pull request uses carry forward flags. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

⚠️ Benchmark changes need a look

🟢 0 better · 🔴 12 worse · ⚪ 3 noise (<±5%) · 0 without baseline

Compared against main 70c2114 benchmarked on this same runner, so the delta is largely free of cross-runner hardware noise. The "7d avg" column still reflects the gh-pages dashboard. Treat <±5% as noise unless repeated.

Dashboard · Run

	config	throughput	MB/s	latency	max Δ latest / 7d
🔴	bs=10 sw=10 sl=64	410	0.25	23,742/34,052/34,052 us	🔴 +19.4% / 🔴 +118.6%
🔴	bs=100 sw=10 sl=64	819	0.5	121,492/146,227/146,227 us	🔴 +11.9% / 🔴 +36.3%
🔴	bs=1000 sw=10 sl=64	951	0.581	1,042,603/1,154,459/1,154,459 us	🔴 +7.9% / 🔴 +12.8%

Baseline details

Latest main 70c2114 from same runner

config	metric	PR	latest main	7d avg	Δ latest	Δ 7d
bs=10 sw=10 sl=64	throughput	410 tuples/sec	458 tuples/sec	787.98 tuples/sec	-10.5%	-48.0%
bs=10 sw=10 sl=64	MB/s	0.25 MB/s	0.279 MB/s	0.481 MB/s	-10.4%	-48.0%
bs=10 sw=10 sl=64	p50	23,742 us	22,520 us	12,593 us	+5.4%	+88.5%
bs=10 sw=10 sl=64	p95	34,052 us	28,526 us	15,579 us	+19.4%	+118.6%
bs=10 sw=10 sl=64	p99	34,052 us	28,526 us	18,786 us	+19.4%	+81.3%
bs=100 sw=10 sl=64	throughput	819 tuples/sec	883 tuples/sec	1,008 tuples/sec	-7.2%	-18.7%
bs=100 sw=10 sl=64	MB/s	0.5 MB/s	0.539 MB/s	0.615 MB/s	-7.2%	-18.7%
bs=100 sw=10 sl=64	p50	121,492 us	114,248 us	100,701 us	+6.3%	+20.6%
bs=100 sw=10 sl=64	p95	146,227 us	130,664 us	107,244 us	+11.9%	+36.3%
bs=100 sw=10 sl=64	p99	146,227 us	130,664 us	116,122 us	+11.9%	+25.9%
bs=1000 sw=10 sl=64	throughput	951 tuples/sec	961 tuples/sec	1,042 tuples/sec	-1.0%	-8.7%
bs=1000 sw=10 sl=64	MB/s	0.581 MB/s	0.587 MB/s	0.636 MB/s	-1.0%	-8.6%
bs=1000 sw=10 sl=64	p50	1,042,603 us	1,041,532 us	981,959 us	+0.1%	+6.2%
bs=1000 sw=10 sl=64	p95	1,154,459 us	1,069,559 us	1,023,080 us	+7.9%	+12.8%
bs=1000 sw=10 sl=64	p99	1,154,459 us	1,069,559 us	1,051,697 us	+7.9%	+9.8%

Raw CSV

config_idx,batch_size,schema_width,string_len,num_batches,total_ms,total_tuples,total_bytes,tuples_per_sec,mb_per_sec,lat_p50_us,lat_p95_us,lat_p99_us
0,10,10,64,20,487.67,200,128000,410,0.250,23741.64,34051.83,34051.83
1,100,10,64,20,2442.53,2000,1280000,819,0.500,121491.99,146226.70,146226.70
2,1000,10,64,20,21023.58,20000,12800000,951,0.581,1042602.53,1154459.33,1154459.33

[Yicong-Huang]

I am converting this PR to a draft: please follow our PR template and mark it ready for review.

[carloea2]

The description now follows the current template, and this is ready for review.