Fix C++ int type mismatch warnings in core/ops files

[mhucka]

PR #476 (dating from 2021) aimed to resolve numerous warnings emitted by the C++ compiler. Most have already been resolved since the time the PR was written, but some still remained. This PR addresses most (possibly all) the rest that can be addressed. (Some cannot be addressed directly because they come from other libraries.)

All of these concern the core ops (tensorflow_quantum/core/ops/) and all the warnings are essentially in the same category of thing, so while this PR touches many files, it seems appropriate to handle them together:

• Changed the data type of variables max_num_qubits and min_num_qubits from int to uint64_t to match the underlying data structures and vector iterations where they were being used.

• Changed the data types of some iterator and limit variables (int q_ind, int64_t q_ind, int nq, and int largest_nq) to uint64_t to resolve compiler warnings when evaluated against the updated max_num_qubits mentioned above.

• Changed the data type of output_dim_size from int to size_t where this variable was directly assigned the result of maps.size() and similar standard library size methods.

• Retained the data types of variables like max_psum_length have been left as int because they interface with Protobuf sizes, which are signed ints.

• In configure.sh, removed -Wno-unused-but-set-variable from the flags used during builds of tensorflow_quantum/core/ops/noise/tfq_.*, since the underlying reason for the warnings has been addressed by this PR.

[mhucka]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors various quantum simulation kernels to use 64-bit integers for qubit counts and dimensions, and removes compiler warning suppressions in the configuration script. Feedback highlights several remaining overflow risks, specifically recommending the use of 64-bit literals for bit-shifts and int64_t for loop indices and lambda parameters in parallelized workloads to handle large batch sizes safely.

[mhucka]

/gemini review

[gemini-code-assist]

Code Review

This pull request updates multiple quantum operations to use 64-bit integers for qubit counts, loop indices, and parallel work parameters to prevent overflow and support larger simulations. Feedback focuses on ensuring consistency by updating batch index variables to int64_t where they are derived from 64-bit loop indices. The reviewer also noted that tfq_adj_grad_op.cc was missed in the type update and suggested a performance optimization in tfq_calculate_unitary_op.cc to hoist a repeated bit-shift calculation out of a hot loop.

[mhucka]

/gemini review

[gemini-code-assist]

Code Review

This pull request performs a comprehensive refactoring of integer types across the codebase, replacing 32-bit integers with 64-bit equivalents (int64_t, uint64_t, and size_t) for qubit counts, loop indices, and tensor dimensions. These changes help prevent potential overflows and improve type safety in simulation kernels. Additionally, the PR removes obsolete compiler warning suppressions in configure.sh and corrects minor typos in source comments. There are no review comments to address, and I have no further feedback to provide.