feature: add IBM Heron R2 device profile with calibration specs

[Prashik123]

Closes #15

Description:
This PR introduces the HeronR2() device profile, allowing users to benchmark Stretto compiled control pulses against the error rates and gate times of IBM's previous generation hardware (ibm_fez, ibm_kingston, ibm_marrakesh).

UnitaryHACK Note:
@kateebonner I noticed this issue was unassigned and the UnitaryHACK 2026 deadline is rapidly approaching today! I sourced the median values and built the profile out fully. If the implementation is solid and you merge it, please assign the issue to me so the bots can officially track the bounty!

Implementation Details:

1. Created HeronR2() in src/profiles.jl modeling the 156-qubit heavy-hex architecture as an 8-qubit linear chain to seamlessly match the HeronR3() standard.
2. Sourced the median calibration parameters: T1 ≈ 218 μs, T2 ≈ 264 μs, and CZ duration = 68.0 ns with an error of 2.848×10⁻³ per arXiv:2410.00916.
3. Sourced hardware-level properties directly from the IBM Quantum platform for ibm_fez/ibm_kingston (Median freq ≈ 5.05 GHz, Anharmonicity ≈ -330 MHz, Coupling J ≈ 3 MHz).
4. Added an isolated @testitem in test/runtests.jl confirming compile_block(qft_circuit(2), HeronR2(), [1, 2]) successfully returns a BlockResult with a bounded mathematical fidelity.

[jack-champagne]

We have many quality submissions and it was a tough decision, but there is still so much work to do on this package and we encourage everyone who made a submission to continue contributing and making suggestions, PRs, and issues on this repo. Thank you all!