fix(optim): reject bias_correction and adam_w_mode in LAMB

[ConnorMoss02]

Problem

LAMB, LAMB8bit and LAMB32bit accept bias_correction and adam_w_mode, but neither reaches the base optimizer: the constructors never pass them to super().__init__(). The update applies bias correction and AdamW-style decay regardless, so a non-default value is silently ignored.

Reproduced on CPU, 5 steps, identical seeds:

class         bias_correction T vs F    adam_w_mode T vs F
LAMB                        0.000000              0.000000
LAMB8bit                    0.000000              0.000000
LAMB32bit                   0.000000              0.000000

control: LAMB max_unorm 1e-4 vs 10.0  ->  max|diff| = 0.499796

The control uses max_unorm, which does reach the optimizer, to show the harness detects a real difference.

Fix

Raise on bias_correction=False and adam_w_mode=False in all three classes, mirroring the amsgrad guard already in this file.

Notes

• No public API changes. The guards only reject values that were already silently ignored, and no code in the repo constructs these classes with them.
• The bias_correction1 / bias_correction2 names in the Triton kernels are local variables computing the correction unconditionally; they do not read this flag.

Tests (tests/test_optim.py)

test_lamb_rejects_unsupported_flags, parametrized over the three classes and both flags. Defaults still construct. All six cases fail with the source reverted.

pre-commit run --all-files passes; 15 LAMB tests pass.

Relates to #1261. Same class as #2085, which covers nesterov and dampening in SGD and LARS; the two are independent and can be reviewed separately.