MNT: Enable numpy 2+ installs (#758)

Numpy 2 is more strict about the overflow math calculations, so
we needed to update a few cases to handle that as well.

imap_processing/cdf/config/imap_hi_variable_attrs.yaml

@@ -287,7 +287,6 @@ hi_de_nominal_bin:
   <<: *default_uint8
   CATDESC: Corresponding histogram angle bin for this Direct Event
   FIELDNAM: Histogram Bin Number
-  FILLVAL: 511
   FORMAT: I2
   LABLAXIS: Hist Bin \#
   VALIDMIN: 0

imap_processing/mag/l1a/mag_l1a_data.py

@@ -336,6 +336,10 @@ def to_signed16(n: int) -> int:
         primary_vectors = []
         secondary_vectors = []
 
+        # To avoid overflows, we need to cast the potentially 8 bit signed integers to
+        # int32 before the bitshifting operations below.
+        vector_data = vector_data.astype(np.int32)
+
         # Since the vectors are stored as 50 bit chunks but accessed via hex (4 bit
         # chunks) there is some shifting required for processing the bytes.
         # However, from a bit processing perspective, the first 48 bits of each 50 bit

pyproject.toml

@@ -38,7 +38,7 @@ space_packet_parser = ">=4.2.0"
 spiceypy = ">=6.0.0"
 xarray = '>=2023.0.0'
 pyyaml = "^6.0.1"
-numpy = "^1.26.4"
+numpy = "<=3"
 
 # Optional dependencies
 numpydoc = {version="^1.5.0", optional=true}