docs: dev blog, performance examples, and compiled 3.3.0 release notes (#4191)

Adds a development blog to the documentation site with a 3.3.0 release
post covering the FusedCodecPipeline and sharded partial-read
coalescing, plus two runnable examples referenced by the post
(examples/codec_pipeline_performance, examples/sharding_coalescing).

Compiles every pending changelog fragment into a single 3.3.0 release
notes section dated 2026-07-30, merging it with the section compiled
earlier in #4148, and empties changes/ — making this commit suitable to
tag as v3.3.0.

Assisted-by: ClaudeCode:claude-fable-5

Author: d-v-b