reduce MSRV to 1.74.0

We increased our MSRV to 1.78.0 because (a) we needed 1.70 or higher for
libfuzzer, and (b) LWK is using 1.78.0.

However, we don't expect LWK to be the primary user of this crate -- if we
want to copy somebody, we should copy rust-bitcoin, who recently moved up
from 1.63 to 1.74.

Author: apoelstra

Cargo.toml

@@ -8,7 +8,7 @@ repository = "https://github.com/BlockstreamResearch/rust-simplicity/"
 documentation = "https://docs.rs/simplicity-lang/"
 description = "General purpose library for processing Simplicity programs"
 edition = "2021"
-rust-version = "1.78.0"
+rust-version = "1.74.0"
 
 [features]
 base64 = ["bitcoin/base64"]

README.md

@@ -115,7 +115,7 @@ and undergoing rapid development. We especially welcome improvements in:
 
 ## Minimum Supported Rust Version
 
-The MSRV of this crate is **1.78.0**. For now we will not increase this without
+The MSRV of this crate is **1.74.0**. For now we will not increase this without
 a major version bump, though as the library matures we may change that policy.
 
 ## Updating libsimplicity

clippy.toml

@@ -1,4 +1,4 @@
-msrv = "1.78.0"
+msrv = "1.74.0"
 
 # Default 250, not sure what units. But it does not like the generic node stuff.
 type-complexity-threshold = 1000

fuzz/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "simplicity-fuzz"
 edition = "2021"
-rust-version = "1.78.0"
+rust-version = "1.74.0"
 version = "0.0.1"
 authors = ["Generated by fuzz/generate-files.sh"]
 publish = false

fuzz/generate-files.sh

@@ -12,7 +12,7 @@ cat > "$REPO_DIR/fuzz/Cargo.toml" <<EOF
 [package]
 name = "simplicity-fuzz"
 edition = "2021"
-rust-version = "1.78.0"
+rust-version = "1.74.0"
 version = "0.0.1"
 authors = ["Generated by fuzz/generate-files.sh"]
 publish = false

simplicity-sys/Cargo.toml

@@ -7,7 +7,7 @@ repository = "https://github.com/BlockstreamResearch/rust-simplicity/"
 documentation = "https://docs.rs/simplicity-sys/"
 description = "FFI bindings to libsimplicity"
 edition = "2021"
-rust-version = "1.78.0"
+rust-version = "1.74.0"
 build = "build.rs"
 links = "rustsimplicity_0_5"