Fix LAS specification violations

[bloom256]

Summary

Fix LAS specification violations and reduce memory usage when exporting LAZ files in core/include/export_laz.h.

Fixes #352
Fixes #358

Changes

LAS spec compliance fixes

• Fix float scale factor: constexpr float scale = 0.0001f produced 0.000099999997474 in the header due to single-precision limitations. Changed to double.
• Fix bounding box in exportLaz(): Manual min/max computation from raw doubles didn't match quantized coordinates written to the file, causing points to fall outside the header bounding box. Replaced with laszip_update_inventory().
• Fix bounding box in save_processed_pc(): adjustHeader() only transformed 2 of 8 AABB corners, producing an incorrect bounding box when the pose contains rotation. Removed adjustHeader() and replaced with laszip_update_inventory().
• Set return fields: return_number and number_of_returns were 0, which is invalid per LAS 1.2 spec (valid range: 1-5). Set both to 1 (single return).

High memory usage fix

• Add LazWriter helper class: RAII wrapper around the laszip writer lifecycle (open, writePoint, close). Centralizes LAZ writing logic so multiple callers share the same correct implementation.
• Refactor exportLaz() to use LazWriter: Signature unchanged — all 22 callers across 13 files are unaffected.
• Refactor save_all_to_las() to stream via LazWriter: Previously copied the entire point cloud into three temporary vectors (pointcloud, intensity, timestamps) before writing. For 218M points this duplicated ~7 GB in memory. Now streams points directly to laszip one at a time — only one point in flight instead of all points buffered.

lasinfo64 report — before

  scale factor x y z:         0.000099999997474 0.000099999997474 0.000099999997474
  offset x y z:               0 0 0
  min x y z:                  -554.883007132173816 -355.845426140132588 230.440027620015343
  max x y z:                  796.307733734780186 57.01202975172562 412.955472548385046
WARNING: stored resolution of min_x not compatible with x_offset and x_scale_factor: -554.883007132173816
WARNING: stored resolution of min_y not compatible with y_offset and y_scale_factor: -355.845426140132588
WARNING: stored resolution of min_z not compatible with z_offset and z_scale_factor: 230.440027620015343
WARNING: stored resolution of max_x not compatible with x_offset and x_scale_factor: 796.307733734780186
WARNING: stored resolution of max_y not compatible with y_offset and y_scale_factor: 57.01202975172562
WARNING: stored resolution of max_z not compatible with z_offset and z_scale_factor: 412.955472548385046
  return_number       0          0
  number_of_returns   0          0
  gps_time 1756111314071322144440057856.000000 1756115495286343064304484352.000000
WARNING: 2 points outside of header bounding box
WARNING: for return 1 real number of points by return (0) is different from header entry (218337242).
WARNING: there are 218337242 points with return number 0
WARNING: there are 218337242 points with a number of returns of given pulse of 0
WARNING: real max x larger than header max x by 0.000046
WARNING: real min z smaller than header min z by 0.000033

lasinfo64 report — after

  file source ID:             4711
  global_encoding:            1
  version major.minor:        1.2
  point data format:          1
  point data record length:   28
  number of point records:    218337242
  number of points by return: 218337242 0 0 0 0
  scale factor x y z:         0.0001 0.0001 0.0001
  offset x y z:               0 0 0
  min x y z:                  -554.8830 -355.8454 230.4400
  max x y z:                  796.3077 57.0120 412.9555
  return_number       1          1
  number_of_returns   1          1
  gps_time 1756111314071322144440057856.000000 1756115495286343064304484352.000000

Zero warnings. (GPS timestamp scaling is a known issue tracked separately.)