Validate TPU accelerate versions consistently

[lovettsendit]

What

Validate --accelerate_version with packaging.version.Version and convert invalid input into a clear, stable ValueError.

Why

Accelerate supports packaging>=20.0, but packaging.version.parse() handles invalid versions differently across supported releases:

• Packaging 21.3 returns a legacy version object.
• Packaging 22.0 and later raise InvalidVersion.

As a result, accelerate tpu-config currently accepts or rejects the same invalid value depending on the installed Packaging version.

Validation

• Existing latest, dev, and explicit-version behavior remains unchanged.
• Added a focused regression test for invalid versions.
• Verified the proposed behavior under Packaging 21.3 and 22.0.
• Breakcheck exercised 18/18 Packaging call sites with agent-authored fixtures, identified this changed call site, and verified that the repaired call behaves identically across both versions.

Discovered and reproduced with Breakcheck.