Add --email option to export command for email-style patch formatting

[VishalGawade1]

Summary of Changes:
Fixes #318

New Flag: Adds the --email flag to format output with email headers.
Email Headers: Generates headers like From, Date, Subject, and Message-Id for each patch to create an email-style format.
Commit Message and Diff: Includes the full commit message, followed by diffstat and the full diff for each revision.
Default Behavior: If --email is not specified, the command falls back to its standard export functionality without email formatting.

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[williewillus]

Are you sure you didn't commit stuff by mistake? There's 1862 changed files but the functional change is only in one of them.

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[VishalGawade1]

Are you sure you didn't commit stuff by mistake? There's 1862 changed files but the functional change is only in one of them.

Ahh, Apologies for the oversight; I'm not sure how the /venv files ended up getting committed.

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[quark-zju]

There was a Mercurial "patchbomb" extension: https://wiki.mercurial-scm.org/PatchbombExtension

We deleted it since it has no internal use-cases but it can be re-added. If we backport the code, we can maintain a command-line UI familiar to Mercurial users. What do you think?

[VishalGawade1]

Really sorry for being little inactive. Re-adding the 'patchbomb' extension sounds like a good to me. It would provide the email functionality in a way that's familiar to Mercurial users.
I can start looking into backporting the 'patchbomb' extension and see how it can be adapted for Sapling. It might take me a while though but any recommendations on how to proceed would be grateful.