rename to rfc 3873

Author: davidtwco

text/0000-build-std-context.md renamed to text/3873-build-std-context.md

@@ -1,6 +1,6 @@
 - Feature Name: `build-std-context`
 - Start Date: 2025-06-05
-- RFC PR: [rust-lang/rfcs#0000](https://github.com/rust-lang/rfcs/pull/0000)
+- RFC PR: [rust-lang/rfcs#3873](https://github.com/rust-lang/rfcs/pull/3873)
 - Rust Issue: [rust-lang/rust#0000](https://github.com/rust-lang/rust/issues/0000)
 
 # Summary