Port bcdec BC4 and BC5 to Rust

[ScanMountGoat]

• bc4 and bc4s
• bc4 and bc4s float
• bc5 and bc5s
• bc5 and bc5s float
• update test data to include signed variants
• update test data to include float output
• u8 encoding and decoding for signed formats #30
• investigate float decoding on apple silicon