fix(arrow-array): align FFI buffers before validation under force_validate

[bit2swaz]

Which issue does this PR close?

• Closes from_ffi realignment is bypassed under force_validate #10034.

Rationale for this change

from_ffi realigned under-aligned C Data Interface buffers (e.g. an 8-byte aligned Decimal128 from a JVM producer) after consume(). under force_validate, consume()'s build() validates first and rejects the buffer before the realign runs, so spec-legal input errors. reachable via the arrow crate with features = ["force_validate", "ffi"] calling arrow::ffi::from_ffi.

What changes are included in this PR?

• ImportedArrowArray::consume builds through ArrayDataBuilder with align_buffers(true) before validation, matching arrow-ipc's create_array_from_builder
• dropped the now-redundant outer align_buffers() calls in from_ffi / from_ffi_and_data_type.

Are these changes tested?

covered by test_decimal128_under_aligned_round_trip. the issue suggested ungating it under force_validate, but that isn't possible as its fixture is a misaligned ArrayData built with build_unchecked, which validates under force_validate and so rejects the input at construction, before from_ffi runs. the gate stays with a comment explaining why

Are there any user-facing changes?

no public API change. behavior only changes under force_validate, where spec-legal under-aligned input is realigned instead of erroring.

[Jefffrey]

how is this change tested if the test already passes on main?

[bit2swaz]

it passes on main because arrow-array's force_validateis empty and doesnt turn on the validation that lives in arrow-data:

arrow-rs/arrow-array/Cargo.toml

Line 72 in d6b0bd7

force_validate = []

so in the arrow-array test job the misaligned buffer is never rejected, with or without this change. the validation only actually runs when arrow-data/force_validate is on which only happens thru the arrow meta-crate's force_validate (it forwards to both crates) and that job doesnt run arrow-array's unit tests. so factually speaking today no CI config runs this test with the validation enabled

and being honest with you: i really couldnt find a way to write a test that exercises the fix under arrow-data/force_validate. the test has to hand from_ffi a buffer thats under aligned for its type. the only way to get one is an ArrayData from build_unchecked but under force_validate that validates anyway (the gate ignores skip_validation), so the fixture is rejected at construction, before from_ffi runs

arrow-rs/arrow-data/src/data.rs

Lines 2267 to 2268 in d6b0bd7

	if !skip_validation.get() || cfg!(feature = "force_validate") {
	data.validate_data()?;

you cant source it from a valid array either: to be under aligned for the import type youd need a source type with the same byte width but smaller alignment and no arrow primitive fits that (align_of == size_of). so the misaligned input is genuinely unconstructable in a force_validate build

what is covered: normal builds run the realignment test. under arrow-data/force_validate the full ffi test module still passes since valid arrays go through the same align-before-validate path in consume so the reorder doesnt break anything. the one gap is the under aligned case under force_validate which is the case that cant be built based on my research

so i can realistically think of two options: leave it as is with the gate and the comment explaining why, or i hand build the FFI_ArrowArray from a raw under aligned pointer in the test to bypass ArrayData entirely and get real coverage, but at the cost of more unsafe test code.

which would you prefer?