Bump Julia lower bound to v1.10 and modernize dependencies

[ChrisRackauckas-Claude]

Summary

• Updates Julia lower bound from 1.6 to 1.10
• Modernizes package dependencies by dropping older lower bounds
• Removes VERSION checks for Julia versions < 1.10
• Updates CI to test on lts, 1, and pre

Changes

Project.toml

• Julia: 1.6 → 1.10
• BenchmarkTools: 0.5 → 1
• Compat: 3.40, 4 → 4
• FiniteDifferences: 0.10 → 0.12
• StaticArrays: 0.11, 0.12, 1 → 1

CI Configuration

• Test matrix: ["1", "min"] → ["lts", "1", "pre"]
• Docs workflow: Julia 1.6 → 1.10

Test Suite

Removed VERSION checks that are no longer needed:

• test/rule_definition_tools.jl: Removed Julia 1.7 LoadError handling
• test/projection.jl: Removed Julia 1.6 and 1.7 version checks
• test/tangent_types/structural_tangent.jl: Removed Julia 1.2, 1.5, and 1.9 checks
• test/tangent_types/thunks.jl: Removed Julia 1.2 checks

Rationale

Requiring Julia 1.10+ allows us to:

• Assume package extensions always exist
• Remove compatibility code for older Julia versions
• Use modern Julia features without version checks
• Align with the current LTS version (1.10)

Test plan

• Tests pass locally on Julia 1.11.6
• CI passes on all platforms
• Documentation builds successfully

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.49%. Comparing base (d42e8ef) to head (468f8a7).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #697      +/-   ##
==========================================
+ Coverage   93.46%   93.49%   +0.03%     
==========================================
  Files          14       15       +1     
  Lines         994      999       +5     
==========================================
+ Hits          929      934       +5     
  Misses         65       65              

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