feat: show templ CLI and go.mod version mismatch warning

[a-h]

Fixes #249

[kron4eg]

After recent update of Go and running go mod tidy my go.mod looks like this:

diff --git go.mod go.mod
index d33db29..76bfbda 100644
--- go.mod
+++ go.mod
@@ -2,8 +2,10 @@ module exp2

 go 1.21.4

+toolchain go1.21.5
+
 require (
-       github.com/a-h/templ v0.2.476
+       github.com/a-h/templ v0.2.501

Which results to the error:

(✓) Generated code for 2 templates with 0 errors in 2.108317ms
(!) templ version check failed: failed to parse go.mod file: <...>/src/backend/go.mod:3: invalid go version '1.21.4': must match format 1.23
<...>/src/backend/go.mod:5: unknown directive: toolchain

[a-h]

Ah yes, just noticed it. Sorry about that... #355

I think the temp solution while the go module parser issue is open is to regexp out the final part of the version before parsing.

I might have time to do that tomorrow and put out a tiny release.