Reorganize query-engine languages and inline OTLP bridge

[marcsnid]

Change Summary

Renames the opl crate to query-engine-languages and nests OPL as a submodule inside it. Adds the OTTL parser stub (from experimental/query_engine/ottl-parser) as a second submodule, giving us a single home for language parsers going forward. Also pulls engine-recordset-otlp-bridge directly into recordset_kql_processor as a local otlp_bridge module so contrib-nodes doesn't depend on that external crate anymore.

All existing tests pass, no behavior changes.

What issue does this PR close?

• Closes Reorganize query-engine related code and language parsers #2743

How are these changes tested?

Existing unit tests cover all moved code. cargo xtask check passes (structure, fmt, clippy, full test suite).

Are there any user-facing changes?

No.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.69%. Comparing base (74bcd98) to head (c8db8bc).

❌ Your project check has failed because the head coverage (80.69%) is below the target coverage (85.00%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (74bcd98) and HEAD (c8db8bc). Click for more details.

HEAD has 5 uploads less than BASE

Flag	BASE (74bcd98)	HEAD (c8db8bc)
	8	3

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2797       +/-   ##
===========================================
- Coverage   86.09%   80.69%    -5.40%     
===========================================
  Files         694      166      -528     
  Lines      263431    48645   -214786     
===========================================
- Hits       226788    39252   -187536     
+ Misses      36119     8869    -27250     
  Partials      524      524               

Components	Coverage Δ
otap-dataflow	∅ <ø> (∅)
query_abstraction	80.61% <ø> (ø)
query_engine	89.61% <ø> (-1.16%)	⬇️
otel-arrow-go	52.45% <ø> (ø)
quiver	∅ <ø> (∅)

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[lquerel]

LGTM