chore: bump msrv

[theochap]

Description

Bump the rust msrv. I doubled checked with succinct and risc0 teams that this version was supported by their respective zkvms

[Copilot]

Pull request overview

This PR bumps the Minimum Supported Rust Version (MSRV) from 1.88 to 1.91, with verification from the succinct and risc0 teams that this version is supported by their respective zkVMs.

Changes:

• Update Rust version from 1.88 to 1.91 in both toolchain and workspace configuration files

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
rust-toolchain.toml	Updates the Rust toolchain channel from 1.88 to 1.91
Cargo.toml	Updates the workspace-level rust-version field from 1.88 to 1.91

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.9%. Comparing base (5a4457f) to head (36eef68).
✅ All tests successful. No failed tests found.

❗ There is a different number of reports uploaded between BASE (5a4457f) and HEAD (36eef68). Click for more details.

HEAD has 20 uploads less than BASE

Flag	BASE (5a4457f)	HEAD (36eef68)
proof	7	0
unit	2	1
e2e	12	0

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