Add a16w8 per-op test for reciprocal

Summary:
Add int16 activation / int8 weight (a16w8) quantization tests for `aten.reciprocal` on Ethos-U55 and Ethos-U85.

## Context
The `reciprocal` op is the second half of the softmax decomposition (`softmax(x) = exp(x) * reciprocal(sum(exp(x)))`), paired with `exp`. Together they form the attention mechanism in EMG2Pose Conformer models. Like `exp`, this op was implicated in the U85 SNR regression (SEV T267939669) — the division-by-reciprocal path can amplify quantization error when the denominator is itself quantized at int16. Adding dedicated a16w8 coverage isolates reciprocal numerics from the rest of the softmax pipeline.

## Changes
- Add `a16w8_reciprocal_test_parameters` dict with 3 test configurations covering rank-1, rank-2, and rank-3 tensors (all shifted by +0.1 to avoid division near zero)
- Add `test_reciprocal_a16w8_u55_INT` using `EthosU55PipelineINT` with `a16w8_quantization=True, symmetric_io_quantization=True, qtol=128, epsilon=2**-16`
- Add `test_reciprocal_a16w8_u85_INT` using `EthosU85PipelineINT` with same kwargs
- Register `ops/test_reciprocal.py` in `fbcode/` and `xplat/` `targets.bzl`

bypass-pytorch-oss-checks

Differential Revision: D104532357

Author: christine-long-meta

backends/arm/test/ops/test_reciprocal.py

@@ -123,3 +123,42 @@ def test_reciprocal_vgf_quant(test_data: torch.Tensor):
         quantize=True,
     )
     pipeline.run()
+
+
+a16w8_reciprocal_test_parameters = {
+    "rank1": lambda: torch.rand(10) + 0.5,
+    "rank2": lambda: torch.rand(5, 10) + 0.5,
+    "rank3": lambda: torch.rand(2, 5, 10) + 0.5,
+}
+
+
+@common.parametrize("test_data", a16w8_reciprocal_test_parameters)
+@common.XfailIfNoCorstone300
+def test_reciprocal_a16w8_u55_INT(test_data: torch.Tensor):
+    pipeline = EthosU55PipelineINT[input_t1](
+        Reciprocal(),
+        (test_data(),),
+        aten_op,
+        exir_ops=[],
+        a16w8_quantization=True,
+        symmetric_io_quantization=True,
+        qtol=128,
+        epsilon=2**-16,
+    )
+    pipeline.run()
+
+
+@common.parametrize("test_data", a16w8_reciprocal_test_parameters)
+@common.XfailIfNoCorstone320
+def test_reciprocal_a16w8_u85_INT(test_data: torch.Tensor):
+    pipeline = EthosU85PipelineINT[input_t1](
+        Reciprocal(),
+        (test_data(),),
+        aten_op,
+        exir_ops=[],
+        a16w8_quantization=True,
+        symmetric_io_quantization=True,
+        qtol=128,
+        epsilon=2**-16,
+    )
+    pipeline.run()

backends/arm/test/targets.bzl

@@ -37,6 +37,7 @@ def define_arm_tests():
         "ops/test_cos.py",
         "ops/test_to_copy.py",
         "ops/test_exp.py",
+        "ops/test_reciprocal.py",
     ]
 
     # Quantization