Adopt Go 1.26

[karolz-ms]

Go 1.26 has shipped with many improvements https://go.dev/doc/go1.26 , we should adopt it when opportunity arises.

Things that caught my attention that might be helpful for us:

• Generic types can refer to themselves https://go.dev/doc/go1.26#language
• New Buffer.Peek method returns next n bytes from buffer without advancing it
• New errors.AsType funtion is a generic, safer version of errors.As
• New Dialer methods are cancellable (take context.Context)
• On Windows, OpenFile now allows any combination of Windows-specific flags

[karolz-ms]

Also, there is a new Tilt release we should start using.

[karolz-ms]

Done via #98 and #99