Optimize DialogueFeignClient small response reader

[schlosna]

Before this PR

Small responses <= 8KiB would always allocate 8KiB ByteBuffer as InputStreamReader creates a StreamDecoder that allocates a fixed 8192 byte ByteBuffer. This allocation becomes a scalability bottleneck for high throughput RPCs with small responses (think something returning timestamps, locks, authorization results, etc.)

See https://github.com/openjdk/jdk/blob/4c03e5938df0a9cb10c2379af81163795dd3a086/src/java.base/share/classes/sun/nio/cs/StreamDecoder.java#L248

After this PR

==COMMIT_MSG==
Avoid InputStreamReader / HeapByteBuffer overhead for small (less than 8KiB) inputs, see FasterXML/jackson-core#1081 and FasterXML/jackson-benchmarks#9 (comment) for benchmarks showing between 2x and 10x speedup handling deserialization of small values.

==COMMIT_MSG==

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Description

Optimize DialogueFeignClient small response reader

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Pull Request Overview

This PR optimizes the DialogueFeignClient by avoiding InputStreamReader and HeapByteBuffer overhead for small responses (less than 8KiB). The optimization reads the entire response into memory as a string for small payloads, which can be more efficient than stream-based reading for small data.

Key changes:

• Added optimization for small response bodies in the asReader() method
• Updated URL decoding to use StandardCharsets.UTF_8 directly instead of string literal
• Removed unused UnsupportedEncodingException import