Move switch() to C

[Bisaloo]

No description provided.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 77355c5 is merged into main:

• 🚀pkg_load: 4.68ms -> 4.59ms [-3.84%, -0.06%]
• ✔️read_bigendian: 11.7ms -> 11.7ms [-1.18%, +0.41%]
• ✔️read_bool: 11.2ms -> 11.2ms [-0.84%, +0.46%]
• ✔️read_empty: 11.6ms -> 11.5ms [-1.27%, +0.43%]
• ✔️read_float32: 11.2ms -> 11.2ms [-0.46%, +0.91%]
• ✔️read_float64: 11.2ms -> 11.2ms [-0.91%, +0.5%]
• ✔️read_int16: 11.2ms -> 11.1ms [-0.95%, +0.31%]
• ✔️read_int32: 11.2ms -> 11.1ms [-1.32%, +0.07%]
• ✔️read_int64: 11.8ms -> 11.7ms [-1.48%, +0.08%]
• ✔️read_int8: 11.2ms -> 11.2ms [-1.25%, +0.23%]
• ✔️read_npz: 13.5ms -> 13.5ms [-1.16%, +0.71%]
• ✔️read_string: 11.3ms -> 11.3ms [-0.9%, +0.92%]
• ✔️read_structured: 12.2ms -> 12.1ms [-1.14%, +0.22%]
• ✔️read_uint16: 11.4ms -> 11.4ms [-1.44%, +0.69%]
• ✔️read_uint32: 11.9ms -> 11.8ms [-1.69%, +0.42%]
• ✔️read_uint64: 12.4ms -> 12.3ms [-1.44%, +0.27%]
• ✔️read_uint8: 11.3ms -> 11.3ms [-0.93%, +0.91%]
• ✔️read_unicode: 11.3ms -> 11.3ms [-0.74%, +0.76%]
  Further explanation regarding interpretation and methodology can be found in the documentation.