config: support hostnames for additional shred destinations

[esemeniuc]

The additional leader and retransmit shred destinations currently accept only IPv4 endpoints. Allow DNS/NSS host:port values in Firedancer and Frankendancer, such as shred-receiver.example.com:5566

Resolve each configured hostname once at tile startup using the system resolver's first IPv4 result, then reuse the numeric endpoints across shred tiles and child processes. Unresolvable hosts fail startup; DNS changes require a restart. IPv6 remains unsupported. Also prevent long hostnames beginning with an IPv4-looking prefix from bypassing the system resolver

[Copilot]

🟢 Approval recommended

Endpoint validation, startup ordering, cross-tile reuse, and relevant edge cases are implemented consistently and covered by tests.

Pull request overview

Adds hostname support for additional shred destinations while preserving numeric IPv4 behavior.

Changes:

• Parses and resolves host:port endpoints once before tile startup.
• Reuses resolved endpoints across shred tiles and child processes.
• Expands configuration storage, documentation, and resolver tests.

File summaries

File	Description
src/disco/topo/fd_dns_resolve.c	Prevents long IPv4-prefixed hostnames from bypassing DNS.
src/app/shared/test_config_parse.c	Tests validation, resolution, and endpoint reuse.
src/app/shared/fd_config.h	Expands destination buffers for hostnames.
src/app/shared/fd_config.c	Adds endpoint resolution and tile propagation.
src/app/shared/fd_config_private.h	Declares the new internal helpers.
src/app/shared/fd_config_json.c	Updates the configuration layout assertion.
src/app/shared/commands/run/run1.c	Resolves destinations for standalone shred tiles.
src/app/shared/commands/run/run.c	Resolves destinations before startup serialization.
src/app/firedancer/topology.c	Removes numeric-only topology parsing.
src/app/firedancer/config/default.toml	Documents hostname behavior for Firedancer.
src/app/firedancer-dev/commands/forktest/forktest.c	Resolves destinations before forktest startup.
src/app/fdctl/topology.c	Removes numeric-only Frankendancer parsing.
src/app/fdctl/config/default.toml	Documents hostname behavior for Frankendancer.

Review details

• Files reviewed: 13/13 changed files
• Comments generated: 0
• Review effort level: Balanced

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