Remove legacy_session and the deprecated APIs that rely on it

[robert3005]

Deletes legacy_session(), its clippy ban, and the deprecated APIs that still used it or that ArrowSession replaces. Their callers move to the explicit-context or session-based versions.

Deleted:

• ArrayRef::{scalar_at, into_canonical, to_canonical} and Array::<V>::{scalar_at, to_canonical}
• the ToCanonical trait and its clippy bans
• Validity::{is_valid, is_null}
• vortex_arrow::IntoArrowArray and from_arrow_array_with_len
• vortex_arrow::FromArrowArray. Its impls were thin shims over the vortex_arrow::convert::from_arrow_* functions, which stay.
• vortex_arrow::{FromArrowType, TryFromArrowType, ToArrowType}. Use ArrowSession::{from_arrow_schema, from_arrow_field, from_arrow_datatype, to_arrow_schema, to_arrow_datatype} instead.
  • The naive schema and decimal helpers that only backed these traits go with them.
  • So does the bench of the deprecated to_arrow_dtype path.
  • Two tests of the naive schema export's own behaviour are dropped: rejecting a nullable top-level struct, and Binary Variant storage. ArrowSession::to_arrow_schema intentionally behaves differently on both. test_schema_conversion now runs against the session.

[codspeed]

Merging this PR will degrade performance by 15.6%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ 2 benchmarks measured no execution time

Nothing ran under measurement, usually because the compiler removed the code under test. These results are not comparable, so they count as unchanged.

Preventing compiler optimizations

• density_sweep_dense_runs[0.9]
• bench_compare_sliced_dict_primitive[(3333, 10000)]

⚠️ 17 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• decompress[u16, (4000, 256)]
• embedding_runs_expanded_baseline[1536]
• embedding_code_runs_expanded_baseline[4096]
• test_scan[int]
• compress_fsst[(500, 16, 4)]
• test_scan_filter[int_float]
• test_scan_filter[int_str_float]
• decode_primitives[i64, (1000, 8)]
• test_scan_filter[int_str]
• random_i128[0.01]
• …and 7 more

ℹ️ 40 benchmarks have no flame graph

The flamegraph could not be generated because we failed to resolve the symbols in the profiling trace. This happens when we fail to harvest information about language frames.

• test_scan_filter[int]
• test_repeated_scan_scalar_at[int_str_float]
• test_scan_read_all_to_arrow_array[int]
• test_repeated_scan[int]
• test_scan[int]
• test_scan_filter[int_float]
• test_repeated_scan_scalar_at[int]
• test_scan_filter[int_str_float]
• test_repeated_scan_filter[int_str_float]
• test_scan_scalar_at[int]
• …and 30 more

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 4 improved benchmarks
❌ 4 regressed benchmarks
✅ 2400 untouched benchmarks
⏩ 12 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	bench_compare_sliced_dict_primitive[(2000, 10000)]	12.7 µs	67.1 µs	-81.02%
❌	Simulation	density_sweep_dense_runs[0.001]	43.4 µs	61.5 µs	-29.48%
❌	Simulation	random_i8[0.01]	103.3 µs	117.6 µs	-12.12%
❌ ℹ️	Simulation	test_scan_filter[int]	3 ms	3.4 ms	-11.21%
⚡	WallTime	filter_neon[8]	1,368 ns	897 ns	+52.51%
⚡	WallTime	threshold_neon[80]	4.3 µs	3.4 µs	+24.25%
⚡ ℹ️	Simulation	test_repeated_scan_scalar_at[int_str_float]	557.3 µs	488.2 µs	+14.15%
⚡	WallTime	filter_neon[64]	2.1 µs	1.8 µs	+13.99%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing rk/remove-legacy-session-final (7231e0b) with develop (c4afd68)}

Footnotes

1. 12 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩