fix: unify LINSPACE alpha/beta dtype in the arange converter

[SrivastavaKshitij]

Description

Issue #4625 has two parts.

1. Part 1 was solved on main by feat: Allow for users / kv cache to add aliased I/O for inplace operations #4251 and fix: arange converter #4456
2. This PR fixes the second part which relates to dtype mismatch

arange resolves a common value_dtype for the sequence and passes it to each
get_trt_tensor call. get_trt_tensor applies that dtype when it constructs a constant, and
returns a value that is already an ITensor unchanged:

    elif isinstance(input_val, TRTTensor):
        return input_val

So a dynamic start keeps the dtype of its incoming ITensor, while a literal step becomes a
constant of value_dtype. TensorRT asks that the LINSPACE alpha (input 1) and beta
(input 2) have the same type, and reports:

IFillLayer `alpha` and `beta` must have the same type.
`alpha` is of type Int32 but `beta` is of type Int64.

This routes every operand through a small helper that casts after get_trt_tensor, so the
resolved dtype holds for all of them. cast_trt_tensor returns the tensor unchanged when the
dtype already matches, so paths that were already consistent are unaffected.

Issues

Closes #4625

Type of change

• Bug fix (non-breaking change which fixes an issue)

Testing

Three cases with a dynamic bound are covered: an int32 start, an int64 start, and both
bounds dynamic. Of those, only the int64 start works today, because the sequence dtype for
integer operands is already int64 and matches.

Checklist:

• My code follows the style guidelines of this project (You can use the linters)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas and hacks
• I have made corresponding changes to the documentation
• I have added tests to verify my fix or my feature
• New and existing unit tests pass locally with my changes
• I have added the relevant labels to my PR in so that relevant reviewers are notified

[SrivastavaKshitij]

@narendasan @apbose for viz