feat: implement snapshot bootstrapper with cbor download + omnibus ch…

[lowhung]

Description

Adds support for bootstrapping Acropolis from NewEpochState CBOR snapshot files. Downloads and parses snapshots from configured URLs,

Related Issue(s)

#395

How was this tested?

Checklist

• [] My code builds and passes local tests
• [] I added/updated tests for my changes, where applicable
• [] I updated documentation (if applicable)
• CI is green for this PR

Impact / Side effects

No breaking changes. This is an additive change.

New optional config:

[startup]
method = "snapshot"

[module.snapshot-bootstrapper]
network = "mainnet"
data-dir = "./data"

Dependencies added: async-compression, futures-util, reqwest, tokio-util

Reviewer notes / Areas to focus

• snapshot_bootstrapper.rs: Download orchestration and gzip decompression
• main.rs: Two-line addition (import + register)