enhancement(http): add schema-cached HTTP binding serde

[stobrien89]

Description

Adds schema-cached HTTP binding serialization and deserialization.

Changes

• Adds generic SchemaExtension support to smithy-core.
• Adds HTTPBindingSchemaInfo for cached HTTP binding metadata.
• Adds HTTPBindingSerializer, driven directly by generated serialize_members().
• Optimizes the existing HTTPResponseDeserializer using ordered cached bindings.
• Preserves the legacy serialize() path for handwritten inputs.
• Fixes computed response Content-Length handling.
• Requires no code generation changes.

Performance

On an x86 (m7i) benchmark instance, Rest JSON p50 improved by:

• Serialization: 49.7%
• Deserialization: 45.2%
• Overall: 47.5%

Before:

Rest JSON 1
  serialization 
    restJson1_CopyObjectRequest_Baseline                       n=10000  p50=33.94 us
    restJson1_CopyObjectRequest_M                              n=10000  p50=109.66 us
    restJson1_PutObject_S                                      n=10000  p50=38.72 us
    restJson1_PutObject_M                                      n=10000  p50=39.35 us
    restJson1_PutObject_L                                      n=10000  p50=38.91 us
  deserialization 
    restJson1_CopyObjectOutput_Baseline                        n=10000  p50=24.52 us
    restJson1_CopyObjectOutput_M                               n=10000  p50=68.39 us
    restJson1_GetObject_S                                      n=10000  p50=56.43 us
    restJson1_GetObject_M                                      n=10000  p50=57.17 us
    restJson1_GetObject_L                                      n=10000  p50=56.82 us

After:

Rest JSON 1
  serialization
    restJson1_CopyObjectRequest_Baseline                       n=10000  p50=13.85 us
    restJson1_CopyObjectRequest_M                              n=10000  p50=87.23 us
    restJson1_PutObject_S                                      n=10000  p50=17.89 us
    restJson1_PutObject_M                                      n=10000  p50=18.18 us
    restJson1_PutObject_L                                      n=10000  p50=18.06 us
  deserialization 
    restJson1_CopyObjectOutput_Baseline                        n=10000  p50=12.26 us
    restJson1_CopyObjectOutput_M                               n=10000  p50=51.71 us
    restJson1_GetObject_S                                      n=10000  p50=29.00 us
    restJson1_GetObject_M                                      n=10000  p50=28.33 us
    restJson1_GetObject_L                                      n=10000  p50=29.05 us

Each case used 5,000 warmup and 10,000 measured iterations.

Compatibility

• Existing HTTPRequestSerializer usage remains supported.
• Inputs implementing only serialize() use the compatibility fallback.
• Response consumer ordering is preserved.
• Document codecs continue receiving the original schema.

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