chore(l2): do not use docker to compile prover except on releases

[ManuelBilbao]

Motivation

We use docker to generate reproducible guest program elfs. This slows down a lot the compilation time (about 15 minutes in a Mac).

Description

Don't use docker by default but only when releasing binaries. The docker build is triggered by setting the PROVER_REPRODUCIBLE_BUILD env var.

[Copilot]

Pull Request Overview

This PR optimizes the prover compilation process by making Docker usage optional, controlled by the PROVER_REPRODUCIBLE_BUILD environment variable. This significantly reduces compilation time (from ~15 minutes on Mac) during development while maintaining reproducible builds for releases.

Key Changes:

• Docker-based compilation is now opt-in via PROVER_REPRODUCIBLE_BUILD environment variable
• Both RISC0 and SP1 guest program builds conditionally use Docker when the variable is set
• GitHub release workflow automatically sets PROVER_REPRODUCIBLE_BUILD=true to ensure reproducible builds

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
crates/l2/prover/src/guest_program/build.rs	Adds conditional logic to use Docker for guest program builds only when PROVER_REPRODUCIBLE_BUILD is set
.github/workflows/tag_release.yaml	Sets PROVER_REPRODUCIBLE_BUILD=true environment variable to enable reproducible builds for releases

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[github-actions]

Lines of code report

Total lines added: 7
Total lines removed: 0
Total lines changed: 7

Detailed view

+----------------------------------------------------+-------+------+
| File                                               | Lines | Diff |
+----------------------------------------------------+-------+------+
| ethrex/crates/l2/prover/src/guest_program/build.rs | 83    | +7   |
+----------------------------------------------------+-------+------+