SI-29: Remove redundant -tracker- from HTTP and UDP crate names (EPIC #1669)

[josecelano]

Subissue of EPIC #1669 — Overhaul: Packages

Remove the redundant tracker segment from four workspace crate names. The word appears twice in each: once in the prefix and again in the middle.

Current name	Proposed name
torrust-tracker-http-tracker-core	torrust-tracker-http-core
torrust-tracker-http-tracker-protocol	torrust-tracker-http-protocol
torrust-tracker-udp-tracker-core	torrust-tracker-udp-core
torrust-tracker-udp-tracker-protocol	torrust-tracker-udp-protocol

None are published on crates.io (Rule U). Also rename folders: http-tracker-core/ -> http-core/, udp-tracker-core/ -> udp-core/.

Scope

• Rename crate name fields in all 4 Cargo.toml files.
• Rename folders via git mv.
• Update all dependency references in root + consumer Cargo.toml files.
• Update all Rust use imports (snake_case crate names).
• Update AGENTS.md, packages/AGENTS.md, docs/packages.md, EPIC.md, coupling report.

Acceptance Criteria

• Old folders removed; new folders exist.
• No Cargo.toml references old crate names or paths.
• No Rust use import references old snake_case names.
• cargo build --workspace, cargo test --workspace, linter all pass.