doc: add BUMP_TO_JMEOS_1.3.md tracking the 1.3 upgrade plan

[estebanzimanyi]

Summary

Companion to tracking issue #1. Adds an in-tree planning doc at doc/BUMP_TO_JMEOS_1.3.md so contributors can find the bump plan without leaving the repo.

Why a doc and not the bump itself

The MobilitySpark JMEOS-1.3 bump is gated externally on JMEOS#8 merging — that PR ports the JMEOS bindings to wrap the MEOS C API 1.3 and is currently OPEN, BLOCKED on review. Until it lands, MobilitySpark has no upstream JMEOS to pull from. New JARs cannot be built; the actual binary swap cannot happen.

This PR therefore commits the plan (not the code change) so that:

• The plan lives in the tree (not just in a transient issue body).
• When JMEOS#8 merges, contributors have a 4-stage checklist they can follow.
• The reasoning behind the staged approach (and the API-compat risk audit — only 2 JMEOS imports across all of MobilitySpark) is durable.

Doc contents

• What "JMEOS 1.3" actually is (a MEOS C-API version bump, not a JMEOS Maven-version bump).
• How MobilitySpark consumes JMEOS today (vendored JARs in libs/; the pom.xml dependency block is decorative).
• The four stages: JMEOS#8 merges → build new JARs → swap → verify → README pin.
• Effort estimate (~2 hours of MobilitySpark-side work once unblocked).
• Cross-references to JMEOS#8 and the v1.3 fork branch.

What this PR does NOT do

• Replace the JARs in libs/ (they don't exist yet; gated on Stage 1).
• Modify pom.xml (the artefactId typo meos → jmeos is cosmetic since the artefact doesn't resolve; risk of breaking working mvn install:install-file setups argues for leaving it until the binary swap).
• Update the README's MEOS install instructions (gated on Stage 4 once a MEOS 1.3 release tag is confirmed).

Cc

• @GaspardMerten — JMEOS maintainer; PR #8 review.
• @mschoema — JMEOS / MobilityDB.
• @JashanReel — MEOS-API context.
• @estebanzimanyi — visibility.

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