refactor: thread PhysicalOptimizerContext through join_selection stats helpers

[asolimando]

Which issue does this PR close?

• Closes Thread PhysicalOptimizerContext through join_selection stats helpers (CBO extension pattern) #23671.

Rationale for this change

JoinSelection's internal statistics helpers each took separate config: &ConfigOptions
and registry: Option<&StatisticsRegistry> parameters. Any new session-scoped CBO input
to these rules (e.g. #21120) would require touching every helper's signature.

What changes are included in this PR?

Replace the config/registry parameter pair on the internal statistics helpers with a
single context: &dyn PhysicalOptimizerContext, reading context.config_options() and
context.statistics_registry() internally. This is a pure internal signature change: all
affected functions are private or pub(crate), with no cross-crate callers. Behavior is
unchanged.

Are these changes tested?

No new tests; this is a non-functional refactor covered by existing tests
(cargo test -p datafusion-physical-optimizer, the physical_optimizer::join_selection
integration tests, and statistics_registry.slt).

Are there any user-facing changes?

No.

---

Disclaimer: I used AI to assist in the code generation, I have manually reviewed the output and it matches my intention and understanding.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 59.25926% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.58%. Comparing base (a38bb10) to head (809b30b).
⚠️ Report is 45 commits behind head on main.

Files with missing lines	Patch %	Lines
...atafusion/physical-optimizer/src/join_selection.rs	59.25%	2 Missing and 9 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24716      +/-   ##
==========================================
+ Coverage   81.45%   81.58%   +0.12%     
==========================================
  Files        1120     1123       +3     
  Lines      401289   406603    +5314     
  Branches   401289   406603    +5314     
==========================================
+ Hits       326871   331716    +4845     
- Misses      55295    55447     +152     
- Partials    19123    19440     +317     

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[asolimando]

@kosiew a small follow-up of #23651, this is a pure refactor to properly propagate PhysicalOptimizerContext, which is meant to be a convenient way to pass context to physical rules, especially those dealing with CBO, so we can enrich context for statistics propagation without breaking signatures.

I have a question: since it's a pure refactor and it doesn't really alter coverage, I would consider #24716 (comment), wdyt?

Thanks!

[kosiew]

@asolimando, thanks for working on this. The refactor looks good to me. I don't see any blocking issues. I left one non-blocking suggestion around adding focused coverage for the new context-threading boundary.

[kosiew]

Could we add a focused test that calls JoinSelection::optimize_with_context with a custom context and statistics registry where the estimates actually change the join decision? The existing registry SLT covers this through the SessionState path, but a test here would directly exercise the context-threading boundary introduced by this refactor. Not blocking, but I think it would be useful coverage.

[asolimando]

Thanks for your review! It's indeed a good chance to improve coverage on JoinSelection::optimize_with_context itself, I have proposed a test along the line you proposed in 809b30b, let me know if that works for you.

[kosiew]

🚀
@asolimando
Thank you for your contribution.