email: encapsulate bindings within worker::email

[guybedford]

Rather than exposing everything at the root, we should ensure all automated bindgen subsystems are generated within clear generation namespaces.

This moves all the bindings for email into worker::email. Posting now as a patch while 0.8.2 can still be yanked.

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 2 untouched benchmarks

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_{Comparing email-bindings (4f8dba6) with main (3f53db2)}