feat: add RPKI RTR protocol support (RFC 6810/8210)

[digizeph]

Add full support for the RPKI-to-Router (RTR) protocol, enabling downstream clients to communicate with RTR cache servers and fetch Route Origin Authorizations (ROAs).

Models (src/models/rpki/rtr.rs):

• Core enums: RtrProtocolVersion (V0/V1), RtrPduType, RtrErrorCode
• All 10 PDU structs: SerialNotify, SerialQuery, ResetQuery, CacheResponse, IPv4Prefix, IPv6Prefix, EndOfData, CacheReset, RouterKey, ErrorReport
• Unified RtrPdu enum for generic PDU handling
• Helper methods: is_announcement(), is_withdrawal(), timing defaults
• Serde support behind feature flag

Parser (src/parser/rpki/rtr.rs):

• parse_rtr_pdu(): parse PDU from byte slice
• read_rtr_pdu(): read PDU from impl Read
• RtrEncode trait with encode() for all PDU types
• RtrError enum for comprehensive error handling
• Support for v0/v1 differences (EndOfData length, RouterKey)

Testing:

• 37 unit tests covering all PDU types
• Round-trip tests (encode -> parse)
• Version-specific tests (v0 vs v1)
• Error case coverage

Documentation:

• Module-level docs with examples
• New "RPKI RTR Protocol Support" section in lib.rs
• RTR RFCs added to supported RFCs list
• New rtr_client example demonstrating ROA fetching and route validation

Example usage:

cargo run --example rtr_client -- localhost 8282

To start a functional RTR server with Docker:

docker run -it --rm -p 8282:8282 rpki/stayrtr -cache https://rpki.cloudflare.com/rpki.json

[Copilot]

Pull request overview

This PR adds comprehensive support for the RPKI-to-Router (RTR) protocol (RFC 6810 v0 and RFC 8210 v1), enabling downstream clients to communicate with RTR cache servers and fetch Route Origin Authorizations (ROAs).

Key changes:

• Complete implementation of RTR protocol PDU data structures and parsing/encoding logic
• Support for both RTR protocol versions (v0 and v1) with version-specific handling
• Comprehensive test suite with 37 unit tests covering all PDU types and error cases

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/models/rpki/rtr.rs	Core RTR protocol data structures including 3 enums (RtrProtocolVersion, RtrPduType, RtrErrorCode) and 10 PDU structs with helper methods
src/parser/rpki/rtr.rs	RTR PDU parsing and encoding functions with comprehensive error handling and 37 unit tests
src/models/rpki/mod.rs	Module definition for RPKI-related data structures
src/parser/rpki/mod.rs	Module definition for RPKI protocol parsers
src/models/mod.rs	Added rpki module export
src/parser/mod.rs	Added rpki module export
src/lib.rs	Added extensive documentation for RTR protocol support with examples and PDU type table
examples/rtr_client.rs	Complete working example demonstrating RTR client implementation with ROA validation
examples/README.md	Added documentation for rtr_client example
README.md	Added RPKI RTR Protocol Support section with examples
CHANGELOG.md	Added Unreleased section documenting the new RTR protocol feature

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[codecov]

Codecov Report

❌ Patch coverage is 98.00250% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.31%. Comparing base (574a244) to head (26b5d07).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/parser/rpki/rtr.rs	96.59%	32 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #257      +/-   ##
==========================================
+ Coverage   90.50%   91.31%   +0.80%     
==========================================
  Files          81       84       +3     
  Lines       13260    14862    +1602     
==========================================
+ Hits        12001    13571    +1570     
- Misses       1259     1291      +32     

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