Release v29.0.0

This reverts commit f9c1562, which removed Protocol 28 preflight
simulation so that soroban-env-host 28.0.1 and 29.0.1 could resolve
together. The next commit keeps both hosts instead: quickstart's local
network defaults to protocol 28, and with only the protocol 29 host,
simulation there fails with "unsupported protocol version: 28".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

soroban-env-host 29.0.1 depends on soroban-wasmi 0.31.1-soroban.29.0.0, the
same soroban-wasmi build as the protocol 29 host in stellar-core 29.0.0.

soroban-env-host 28.0.1 needs soroban-wasmi 0.31.1-soroban.20.0.1, and Cargo
allows only one semver-compatible version of a crate per source, so both
hosts can't take soroban-wasmi from crates.io. The protocol 28 host is now
pinned by git to rs-soroban-env v28.0.1 (7a7629cf), the commit its crates.io
28.0.1 release was published from; its soroban-wasmi then comes from git
(0ed3f3de, the commit the crates.io 0.31.1-soroban.20.0.1 release was
published from). Apart from the protocol 29 host's soroban-wasmi, neither
host's code changes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

RPC v29.0.1: keep Protocol 28 simulation by pinning the P28 host by git