[codex] prepare v0.7.2 release

[bernalde]

Summary

• Bump MQLib.jl to v0.7.2 for the current JuliaQUBO ecosystem releases.
• Allow QUBOTools 0.15 while retaining QUBOTools 0.13 and 0.14 compatibility.
• Make the QUBODrivers 0.6 compatibility range explicit so resolution can select QUBODrivers 0.6.4.
• Update compatibility metadata tests and changelog release notes.

Registry confirmation

Confirmed in General via gh api:

• QUBOTools v0.15.1 is registered.
• QUBODrivers v0.6.4 is registered and its registry compat allows QUBOTools through 0.15.
• ToQUBO v0.5.1 is registered and its registry compat allows QUBOTools through 0.15 and PseudoBooleanOptimization through 0.3.
• PseudoBooleanOptimization v0.3.0 is registered.

Validation

• git diff --check
• julia --startup-file=no -e '... fresh-depot resolver with MQLib v0.7.2, QUBOTools v0.15.1, QUBODrivers v0.6.4, ToQUBO v0.5.1, PseudoBooleanOptimization v0.3.0 ...'
• julia --project=. -e 'using Pkg; Pkg.test(; coverage = false)'
• julia --startup-file=no -e '... fresh-depot Pkg.test("MQLib") with QUBOTools v0.15.1 and QUBODrivers v0.6.4 ...'
• MQLIB_UPSTREAM_DIR=/tmp/mqlib-upstream.cQalVl bash test/native_c_api_smoke.sh

Docs build was not run because this repository does not have a docs project or Documenter setup.

[bernalde]

@JuliaRegistrator register branch=codex/update-juliaqubo-ecosystem

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