Add --enable-fastdev-unsafe-for-production, subsuming unified buid

[graydon]

This is a proposal for how to address #5267 in the short term. Longer term we might need some more involved fixes, but this should make life much nicer day-to-day for stellar-core devs.

It adds a new mode --enable-fastdev-unsafe-for-production which:

• Is still an optimized mode, but not quite as optimized (it turns off LTO and turns on multiple CGUs)
• Still has debuginfo, but not quite as much (just line tables; enough for profiling and backtraces)
• Turns off all soroban hosts except curr and optionally next (if next is enabled)
• Turns on the "unified build" (it actually subsumes/replaces that flag, since it was mainly useful for this sort of scenario anyways, along with asan and tsan, both of which are mainly useful for testing curr and next)
• Also turns on next, because .. it's simpler to implement / fewer features if it's a superset. Also it doesn't cost much more and next is a very common development configuration anyways.

Results:

Before:

$ time make -j 20 (with warm ccache)
real    6m6.625s
user    12m13.915s
sys     0m57.854s

$ ls -lah src/stellar-core
-rwxr-xr-x 1 dev dev 993M May 28 04:37 src/stellar-core

After:

$ time make -j 20 (with warm ccache)
real    0m42.597s
user    3m35.143s
sys     0m27.528s

$ ls -lah src/stellar-core
-rwxr-xr-x 1 dev dev 277M May 28 04:48 src/stellar-core

[Copilot]

Pull request overview

This PR adds a new unsafe fast development Rust build mode intended to reduce local build time and binary size by using a lighter Rust profile and compiling fewer Soroban host versions.

Changes:

• Adds --enable-fastdev-unsafe-for-production configure/build plumbing.
• Introduces a fastdev Cargo profile and feature.
• Gates older Soroban protocol modules/caches out of fastdev builds and updates docs.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
configure.ac	Adds the fastdev configure option and sanitizer messaging updates.
src/Makefile.am	Wires fastdev into Rust toolchain/profile/features and Soroban protocol selection.
Cargo.toml	Defines the root fastdev Rust profile.
Cargo.lock	Updates locked Soroban/XDR git dependencies.
src/rust/Cargo.toml	Replaces unified feature docs/dependencies with fastdev feature wiring.
src/rust/src/soroban_proto_all.rs	Excludes older hosts in fastdev and adjusts dispatch tests.
src/rust/src/soroban_module_cache.rs	Gates older module caches and dispatches cache operations via selected host module.
src/rust/src/soroban_test_extra_protocol.rs	Gates p22-only test resource modification out of fastdev.
CONTRIBUTING.md	Updates developer documentation from unified Rust builds to fastdev builds.

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