Update Core to v0.5.5 with Sequential support and Eigen 5.0.1

[sdatkinson]

Summary

• update NeuralAmpModelerCore from v0.5.3 to the v0.5.5 candidate plus the upstream Sequential implementation from [FEATURE] Sequential model NeuralAmpModelerCore#323 (d2b2954)
• update the top-level Eigen submodule to 5.0.1 (bc3b398), matching Core and superseding Update NeuralAmpModelerCore to 0.5.4 and Eigen to 5.0.1 #650
• add the new Core translation units and headers, including sequential.cpp and sequential.h, to the macOS, iOS, and Windows projects
• rebase onto the latest plugin main

Impact

The plugin recognizes NAM 0.7.0 Sequential models and chains their child DSP models. This fixes loading the Gateway 1.1.0 WaveNet→Linear and LSTM→Linear models while retaining the v0.5.5 Core and Eigen updates.

The Core submodule currently points to the tip of sdatkinson/NeuralAmpModelerCore#323, which is based directly on the current Core main candidate.

Validation

• NeuralAmpModelerCore Release build and run_tests: passed
• loaded deluxe-reverb-atmospheric.nam (WaveNet→Linear): passed
• loaded deluxe-reverb-vibrato-atmospheric.nam (LSTM→Linear): passed
• macOS VST3 Release universal build and local install: passed
• installed VST3 binary contains the Sequential implementation: verified
• macOS/iOS Xcode project parsing: passed
• Visual Studio project XML validation: passed
• git diff --check: passed
• iOS AUv3 framework build remains blocked by the pre-existing missing NeuralAmpModeler/projects/resample.cpp reference already present on main