[EPIC] v0.2.0: Streaming Support & High-Performance I/O

[Bernardusz]

📃 Description

To support large file transfers and real-time data streaming without memory exhaustion, Levtus needs a coordinated refactor of its I/O layer. This Epic tracks the transition from a "buffered-only" engine to a "streaming-first" engine.

📑 Requirements:

[ ] Core: Implement bodyStream() for Request (OOM Protection)
[ ] Protocol: Add 100-Continue Handshake (Bandwidth Efficiency)
[ ] Routing: Implement Route-specific maxBodySize overrides
[ ] Performance: Add Zero-Copy ctx.file() response support
[ ] Compliance: Implement Chunked Transfer Encoding (RFC 9112)

🚩Constraint

1. Stick to the philosophy, no dependency
2. All I/O must be blocking-compatible for Virtual threads, and avoid synchronized blocks that pin threads.
3. The engine must never buffer more than 8KB of a request unless explicitly requested via a config change.
4. Every implementation must strictly follow a specific RFC requirement. A deviation must be documented as a deliberate design choice in the sub-issue.

🌟Target

The end goal should be:

1. User can stream/download data without the server being exhausted by Sloworis or OOM Error.
2. The developer can define the maxBodySize for each API; the default should be 10MB.
3. The user can send data in chunks using Chunked Transfer Encoding or in 100-Continue Handshake
4. The .bodyStream() will use a new LevtusInputStream that extends InputStream.
5. The .body() use .bodyStream() method internally and will use as little RAM as possible.

📚 References

README.md
RFIC 9112
CONTRIBUTING.md