xchain-sdk v0.19.0

xchain-sdk v0.19.0, part of the XChain Platform v0.19.0 train.

The SDK encodes XBRIDGE and adds a bridge builder method; XBRIDGE is priced and the
bridge-era ISSUE and DESTROY pre-flight rules are predicted, with plain-English descriptions
for every XBRIDGE version bounded by the cosigner value policy. The ISSUE format 7 bridge
field rules and the reserved-roots list are mirrored by value. A caret ticker reference is
accepted on every ISSUE format the way consensus resolves it and compacted on the edit
formats only, and address-list items validate against the configured network's coins
instead of length alone. @dankest-llc/xchain-sdk and xchain-mcp publish at 0.19.0.
Restructured under the platform code-structure standard; consensus identity byte-identical
and pinned.

Full notes in CHANGELOG.md. The platform release with every component tarball is on xchain-node:
https://github.com/XChain-Platform/xchain-node/releases/tag/v0.19.0