build: lift MSRV to 1.80 workspace / 1.88 node binding

The previous MSRV pins were below what current transitive dependencies
need:

  - rayon-core 1.13.0 (pulled in by the optional `parallel` feature on
    wickra-core via rayon) requires rustc >= 1.80; under the old 1.75
    workspace MSRV the CI MSRV job broke with "package `rayon-core
    v1.13.0` cannot be built because it requires rustc 1.80 or newer".
  - napi-build 2.3.2 (the build-script crate that napi-derive 2.x calls
    into) requires rustc >= 1.88; under the old 1.77 node-binding MSRV
    the CI MSRV-node job broke with "package `napi-build v2.3.2` cannot
    be built because it requires rustc 1.88 or newer".

Pinning the deps backwards would have frozen us out of upstream
security/fix releases for both crates. Lifting the MSRV is the cleaner
path for a young 0.x library — downstream consumers on older toolchains
can stay on the already-published 0.2.0.

Updated:
  - Cargo.toml workspace rust-version 1.75 -> 1.80
  - bindings/node/Cargo.toml rust-version 1.77 -> 1.88
  - .github/workflows/ci.yml MSRV matrix names + toolchain values + comment
  - CHANGELOG.md [Unreleased] documents the bump

bindings/node/Cargo.toml

@@ -4,9 +4,11 @@ description = "Node.js bindings for the Wickra streaming-first technical indicat
 version.workspace = true
 authors.workspace = true
 edition.workspace = true
-# napi-build emits `cargo::` directives that require Rust >= 1.77; the rest of
-# the workspace stays at 1.75 because the core crate has no such dependency.
-rust-version = "1.77"
+# napi-build 2.3.2 requires Rust >= 1.88 (newer than the workspace 1.80
+# minimum, which itself was lifted to satisfy rayon-core 1.13.0). napi-build
+# also emits `cargo::` directives that require >= 1.77 — that older floor is
+# subsumed by the 1.88 requirement now.
+rust-version = "1.88"
 license.workspace = true
 repository.workspace = true
 homepage.workspace = true