Use encodingEntrySize for IndexPir

[fboemer]

Use encodingEntrySize for IndexPir.

We add encodingEntrySize to PirParameters which, when enabled, will prepend each IndexPir entry with a VarInt encoding.
This is useful to support IndexPir with varying entry sizes (unlike in KeywordPIR, where we just 0-pad to make all the entry sizes match).

2 breaking changes detected in PrivateInformationRetrieval:
  💔 API breakage: constructor IndexPirConfig.init(entryCount:entrySizeInBytes:dimensionCount:batchSize:unevenDimensions:keyCompression:) has been removed
  💔 API breakage: constructor IndexPirParameter.init(entryCount:entrySizeInBytes:dimensions:batchSize:evaluationKeyConfig:) has been removed

2 breaking changes detected in ApplicationProtobuf:
  💔 API breakage: func Apple_SwiftHomomorphicEncryption_Api_Pir_V1_PIRShardConfig.native(batchSize:evaluationKeyConfig:) has parameter 1 type change from HomomorphicEncryption.EvaluationKeyConfig to Swift.Bool
  💔 API breakage: func Apple_SwiftHomomorphicEncryption_Api_Pir_V1_PIRShardConfig.native(batchSize:evaluationKeyConfig:) has been renamed to func native(batchSize:encodingEntrySize:evaluationKeyConfig:)

1 breaking change detected in _TestUtilities:
  💔 API breakage: func PirTestUtils.getTestParameter(pir:with:entryCount:entrySizeInBytes:keyCompression:batchSize:) has been renamed to func getTestParameter(pir:with:entryCount:entrySizeInBytes:keyCompression:batchSize:encodingEntrySize:)