Feat: Add major_termination_length parameter

[arnaudon]

This allows one to create an axon with a main branch and collaterals. The main branch is usually cut for local axons, as it propagates to other regions. With this PR, we can have a very long bar for it (so that it is considered as major branch), but not synthesize it entirely, to mimic the local axon reconstructions.

[arnaudon]

@lidakanari @adrien-berchet , this is ready to review, it is a 'minor hidden thing' for hipp axons, so i didn't add tests for now

[codecov[bot]]

Codecov Report

Merging #78 (27736f3) into main (effca74) will increase coverage by 0.00%. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #78 +/- ## ======================================= Coverage 97.69% 97.69% ======================================= Files 39 39 Lines 2166 2172 +6 Branches 373 375 +2 ======================================= + Hits 2116 2122 +6 Misses 30 30 Partials 20 20 ``` | [Flag](https://app.codecov.io/gh/BlueBrain/NeuroTS/pull/78/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain) | Coverage Δ | | |---|---|---| | [pytest](https://app.codecov.io/gh/BlueBrain/NeuroTS/pull/78/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain) | `97.69% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files Changed](https://app.codecov.io/gh/BlueBrain/NeuroTS/pull/78?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain) | Coverage Δ | | |---|---|---| | [neurots/generate/tree.py](https://app.codecov.io/gh/BlueBrain/NeuroTS/pull/78?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain#diff-bmV1cm90cy9nZW5lcmF0ZS90cmVlLnB5) | `98.97% <100.00%> (+0.06%)` | :arrow_up: |

[arnaudon]

Do you plan to add tests in this PR?

nope