Add setRaw() method for Set type encoder (#1086)

[aymenjam]

Problem

getRaw() is generated in the decoder for Set (bitset) types, but the
symmetric setRaw() method is missing from the generated encoder,
preventing direct writes of a raw bitset value without going through
individual choice setters.

Fixes #1086

Solution

Added generation of setRaw() in JavaGenerator#generateBitSet, mirroring
the existing getRaw() decoder logic, using the same generatePut
mechanism already used elsewhere in the generator.

Testing

Added shouldGenerateBitSetRawAccessor in JavaGeneratorTest, which
encodes a raw value via setRaw() and verifies it round-trips correctly
through the existing getRaw() decoder method.

All existing tests pass, including shouldGenerateBitSetCodecs.

[vyazelenko]

Overall looks good. Just minor things with a test.

[aymenjam]

@vyazelenko
Simplified as suggested — thanks for the review!