Turn off some dependencies for library users (#599)

* Enable serialport for cli through its feature

* Add flashing feature, disable feature-specific dependencies

* Make strum optional

* Make toml optional

* Oops

* Changelog

* Merge flashing back into serialport

* Remove rppal mention

* Move things back

* Only enable miette/fancy for the CLI

.github/workflows/ci.yml

@@ -80,7 +80,6 @@ jobs:
     runs-on: ubuntu-22.04
 
     steps:
-
       - uses: actions/checkout@v4
 
       - uses: ./.github/actions/setup-target
@@ -89,6 +88,7 @@ jobs:
           target: ${{ matrix.platform.target }}
 
       - run: cargo check -p espflash --lib --no-default-features
+      - run: cargo check -p espflash --lib --no-default-features --features serialport
 
   msrv:
     name: Check MSRV (${{ matrix.platform.target }})