feat: support RFC 5543 traffic engineering attribute

[downwithbgp]

Fixes #290

Summary

• add structured parsing for the RFC 5543 BGP Traffic Engineering attribute
• expose the Switching Capability, Encoding, Reserved, and eight Maximum LSP Bandwidth fields
• retain switching-capability-specific information as raw Bytes
• support encoding while preserving the opaque capability-specific tail
• wire attribute code 24 into the parser and encoder as optional non-transitive
• add PSC-1, unknown-capability, truncated-input, exact-wire encoding, and round-trip tests
• update the supported-RFC and attribute documentation

Validation

• cargo fmt --check
• cargo check --all-targets --all-features
• cargo test --all-features traffic_engineering
• cargo test --all-targets --all-features

[Copilot]

Pull request overview

Adds first-class support for the RFC 5543 BGP Traffic Engineering path attribute (code 24) to bgpkit-parser, moving it from raw-retained handling to a typed model with structured parsing/encoding while preserving the capability-specific tail as opaque bytes.

Changes:

• Introduces TrafficEngineering attribute model and wires AttrType::TRAFFIC_ENGINEERING into attribute parsing/encoding and flag validation.
• Implements RFC 5543 fixed-header parsing/encoding with raw retention of switching-capability-specific trailing bytes.
• Adds unit tests for PSC-1, unknown capability retention, truncated input, and exact-wire round-trip; updates supported-RFC and attribute documentation.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/parser/mrt/mrt_elem.rs	Includes TrafficEngineering in the relevant attribute set for MRT elements.
src/parser/bgp/attributes/README.md	Updates attribute support tables to mark Traffic Engineering as implemented and fixes reference formatting.
src/parser/bgp/attributes/mod.rs	Wires TRAFFIC_ENGINEERING into parsing/encoding, removes it from raw-retained list, and validates flags as optional non-transitive.
src/parser/bgp/attributes/attr_24_traffic_engineering.rs	New parser/encoder implementation for RFC 5543 attribute (fixed portion + opaque tail) with comprehensive tests.
src/models/bgp/attributes/mod.rs	Adds TrafficEngineering struct + enum variant and integrates type/category/flags behavior.
src/lib.rs	Documents RFC 5543 typed attribute support in crate docs (source for README generation).
README.md	Reflects updated generated documentation including RFC 5543 support.

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[digizeph]

Good work, thanks for the contribution!